Early Roman Mosaic Materials in Southern Britain, J.R.L, Allen, M.G, Fulford

Early Roman Mosaic Materials in Southern Britain, with Particular Reference to Silchester(Calleva Atrebatum): A Regional Geological PerspectiveAuthor(s): J. R. L. Allen and M. G. FulfordSource: Britannia, Vol. 35 (2004), pp. 9-38Published by: Society for the Promotion of Roman StudiesStable URL: http://www.jstor.org/stable/4128620Accessed: 06/12/2008 10:42

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Early Roman Mosaic Materials in

Southern Britain, with Particular

Reference to Silchester

(Calleva A trebatum): a Regional Geological Perspective

By J.R.L. ALLEN and M.G. FULFORD

With a Palaeontological Note by J.A. Todd and N.J. Morris

INTRODUCTION

Mosaics represent one of the best known art forms in the Roman world. Their geometric patterns and designs, their figurative images, and their development through time have been extensively studied, and corpora have been assembled for certain provinces of the

Empire.' In Britain, the study of the surviving mosaics has led to the identification of certain late Roman 'schools' (stylistic groupings) of mosaics on the basis of shared stylistic attributes.2 Now it will be possible to place this work in a fuller context as the long-awaited corpus of all Roman mosaics known from Britain begins to appear.3 However, whereas the late mosaics undoubtedly show considerable regional distinctness, the position of the earliest work that pioneered the form in Britain is far less clear, perhaps because mosaics of the first and early second century A.D. are fewer and have excited much less interest.

If the emphasis up to now has been on the mosaic, whether complete or fragmentary, too little attention has, perhaps, been focused on the materials, especially the tesserae, individually or collectively, which in their hundreds of thousands make up each floor. To what extent did the artist search out his materials, rather than simply exploit whatever was made available to him? To what extent is the style of a mosaicist revealed not just by stylistic features, but by the choice of materials and the way they were fashioned into shape? Would a metrical study of the individual tesserae and a quantitative evaluation of the different materials used help to characterise an individual's work? How did mosaicists fare in regions where suitable natural materials were limited? The potential range of geological and artificial materials which could be used to form tesserae is large, and the evidence currently embraces local or imported stone or marble types and ceramics such as tile/ brick or pottery, e.g. oxidised sigillata or reduced grey-black kitchen wares. Glass, too, whether

1 Dunbabin 1999, esp. 88-100 for Britain; Ling 1998. (See also Corpus de Mosaicos de Espahia from 1978; Mosa'ques de Tunisie from 1973; and Receuil ge'ne'ral de mosai'ques de la Gaule).

2 For second-century A.D. schools: Smith 1975, esp. 276-7; Smith 1984, esp. 362-4. For fourth-century A.D. schools: Smith 1965; Smith 1969, esp. 95-113; Smith 1984, 366-76; Johnston 1977; Smith's approach has been criticised by Ling (1997, 264-9) and new work on defining stylistic groupings has been taken forward in the context of the British corpus by Neal and Cosh 2002, 20-9.

3 Neal and Cosh 2002.

? World copyright reserved. Exclusive Licence to Publish: The Society for the Promotion of Roman Studies 2004

10 J.R.L. ALLEN AND M.G. FULFORD

deliberately fashioned as tesserae, or from discarded vessels, is found. Coloured slags may also have been exploited.

Individual tesserae or larger assemblages may not have the same aesthetic appeal as the mosaic pavement itself, but the aim of this paper is to consider what can be deduced from a large assemblage of loose tesserae from a known site and early context. In the first place, the analysis of the materials with a view to determining their shape characteristics as well as their petrological features and provenance offers a way of linking them with tesserae employed in other mosaics of a similar date but from a different location. This then invites the question whether any shared materials can be equated with shared style and design. Were all the mosaics using the same material made by the same workshop? One further corollary is that it should be possible to develop from the loose tesserae some sense of the style and patterning of the original floors which have otherwise been destroyed. In putting forward evidence that bears on these various questions, we have not attempted to examine every early mosaic that has been reported from Roman Britain, but have concentrated our attention on the region largely to the south of the estuaries of the Thames and Severn, where material survives from a wide and representative range of military and civil constructions.

SILCHESTER INSULA IX

BACKGROUND

Since 1997 excavations have been continuing of an area of some 3000 m2, representing about one-third of Insula IX, immediately to the north-west of the forum-basilica in Silchester (Calleva Atrebatum) in northern Hampshire (FIG. 1).4 The insula was first excavated in 1893-94 and a brief

KEY TO SITES N

0 towns * civil/public * military

Caerleon ri Kmr a ourTdops haomes

LondonAEstuary ENGLCH CAL lSilchester C 1.4NN

4',j?Eccles 100 km

Angmering Exeter CorfeCastle

Fishbourne

Kimmeridge Bay

Ringstead Boy Outcrops of

.Kimmeridge Cloy Formation

N I

CHANN EL Isle of Portland ENGL/SH CHANVNEL

FIG. 1. Distribution of sampled sites with early Roman mosaics and opus sectile in southern Britain.

4 Clarke and Fulford 2002.

EARLY ROMAN MOSAIC MATERIALS IN SOUTHERN BRITAIN 11

report and plan were published.5 The new excavations have not only shown that a very high percentage of the original stratigraphy survived the Victorian excavations, but that the development of the area was complex. As far as the main finding of the original excavation, House 1, is concerned, this can now be shown to conflate a complex development where two masonry houses were constructed as replacements for timber-framed buildings in the later first century A.D., subsequently demolished and then succeeded in the second century A.D. by a larger, hall-like building which occupied in full the site of its predecessors. In its turn this building was demolished no later than the third century A.D. To the south of the two town-houses there are further traces of early Roman buildings which pre-date the late Roman arrangements of the insula but whose remains have yet to be fully excavated.

Of the sequence of masonry buildings thus far excavated no original flooring remained in situ except in the corner of the central room of the northern of the two first-century masonry houses. Here there was a group of tile tesserae which probably once bordered a mosaic. That there were mosaics associated with one or both of these houses, and with the early structures whose excavation has yet to be completed, is implied by the number of tesserae which have emerged in the course of the excavation, and particularly from contexts associated with the demolition of the early buildings and the levelling and make-up of ground prior to the construction of new buildings from the late third century A.D. These can reasonably be assumed to have derived from early Roman buildings dating from the later first century A.D. and destroyed no later than c. A.D. 200-250. Indeed, the earliest examples come from contexts associated with the construction of the masonry houses of the later first century A.D., implying that some at least derive from pre-Flavian floors. A striking feature of these tesserae is both their range of materials and associated colours and, in the case of some materials, their small size and, in the case of others, their extreme variation in size. In trying to develop a plausible impression of the interior decor of our early houses, we have the possibility of linking them with other Silchester mosaics recovered from earlier excavations and stored in the Museum of Reading. In this respect, the fact that our materials have a clear terminus ante quem for their final deposition has an added value, since none of the early finds of mosaics can be related to dated archaeological contexts. At least through our materials we have the possibility of providing the first foundations toward a chronological framework for the Silchester mosaics.

Excluding very large tesserae of broken brick or tile used for containment borders, which were not systematically examined, a total sample of 1,309 whole or broken/weathered tesserae resulted from the 1997-2003 excavations (Table 1). Yields were very low in the higher contexts at Insula IX but increased by an order of magnitude in the lower levels. A significant proportion of the tesserae, coming from a range of dated but chiefly early contexts, carried traces of a white, sandy mortar and, in a few cases, of opus signinum, and it was often clear that these had been smoothed by wear on one face. Among the collections was a small fragment from an actual mosaic (see below). Although on a proportion of the tesserae it may not have survived, most tesserae lacked traces of mortar, and appeared fresh and unused. All tesserae were examined using a hand-lens, and representative samples were thin-sectioned for microscopic examination and some powdered for mineralogical analysis by x-ray diffraction. The tesserae fall into 22 categories of lithology or fabric, divided between six groups: sandstones (S), rocks dominated by carbonate minerals (L), flint (F), burnt mudrocks (M), ceramic (C), and miscellaneous (X). By number, one fabric (La) comprises c. 71 per cent of the assemblage, while another (Mc) contributes c. 17 per cent. The remaining fabrics are largely present to the extent of less than 1 per cent each.

SANDSTONE TESSERAE

Lithology Sa is an off-white to pale grey, fine- to medium-grained quartz sandstone to quartzose limestone with variable amounts of coarse shell and other skeletal debris, pellets of microcrystalline

5 Fox 1894.


TABLE 1. COMPOSITION OF SAMPLE OF TESSERAE FROM INSULA IX, SILCHESTER.

Category No. % Category No. % Sandstones Flint Sa 23 1.76 Fa 4 0.31 Sb 27 2.06 Fb 2 0.15 Sc 1 0.08 Subtotal 6 0.46 Sd 1 0.08 Subtotal 52 3.98 Ceramic

Ca 25 1.91 Carbonate rocks Cb 5 0.38 La 924 70.59 Cc 3 0.23 Lb 17 1.30 Cd 1 0.08 Lc 2 0.15 Ce 1 0.08 Ld 1 0.08 Cf 2 0.15 Subtotal 944 72.12 Cg 1 0.08

Subtotal 38 2.91 Burnt mudrocks Ma 42 3.21 Miscellaneous Mb 6 0.46 Xa 2 0.15 Mc 217 16.58 Xb 2 0.15 Subtotal 265 20.25 Subtotal 4 0.30

Grand totals 1309 (100.02%)

calcite, and an abundant calcareous cement. Thin oolitic coatings cover many of the carbonate grains and also some of the quartz. The quartz is subrounded to well rounded and very well sorted. There are scattered grains of plagioclase feldspar and microcline, and a little fresh to partly oxidised glauconite. This lithology is represented by very large, cuboidal tesserae that measure 25-35 mm along the side and were probably used in borders. One tessera includes a well preserved trace fossil, kindly identified by Dr R. Goldring (University of Reading) as Diplocraterion habichi, known from the Jurassic rocks of Britain and the North Sea, and the Tertiary beds of Spain.6 Others are coarsely laminated. The provenance of this lithology is unknown. So far as a possible source in the Mesozoic rocks of southern England is concerned, however, the small amount of glauconite suggests a date not earlier than the latest Jurassic.

The lithology Sb is a very hard, reddish black to black, medium- to coarse-grained, ferruginously cemented sandstone dominated by well rounded and sorted quartz. It too occurs only as very large, cuboidal tesserae that would have been used in borders. They were cut from naturally worn, platy lumps of the rock, probably collected from a Pleistocene fluvial gravel deposit. The naturally worn surfaces that survive on many of these tesserae are smooth, polished, and, in some instances, faintly dimpled as if sculptured by wind-blown sand on a gravel plain devoid of protecting vegetation. The whereabouts of the gravels is unknown, but the rock itself suggests an ultimate provenance in either the early Cretaceous of the southern English Midlands or perhaps the Tertiary of the Hampshire Basin.

A soft, light yellow, very fine-grained, slightly micaceous quartz sandstone is assigned to lithology Sc. It is represented by a single tessera, of normal size (for Silchester, see modular tessera in FIG. 2A). Lacking macroscopic distinguishing features, it is not possible to suggest a provenance.

Lithology Sd, also represented by a single normal-sized tessera, is of a soft, greyish brown, slightly micaceous, very coarse quartz siltstone to very fine sandstone. The provenance is unknown.

6 Goldring et al. 1998, 361-3, 370.


CARBONATE TESSERAE

Overwhelming all other categories in the collections, lithology La is in hand-specimen a very variable, weakly effervescent, finely granular carbonate rock that ranges in colour on the surfaces of tesserae from light yellowish grey to yellowish black, depending on soil conditions. The bedding is evident on the paler surfaces as scattered to very abundant, parallel streaks of black organic matter. On broken surfaces, however, the rock is dark yellowish to brownish grey, and in badly weathered examples borders on ginger. Several tesserae contained poorly preserved marine fossils, notably oyster spat and the bones, especially the skulls, of small fish. These fossils are not stratigraphically diagnostic, other than supporting a broad Mesozoic-Tertiary age (see Palaeontological Note below).

In thin-section under the microscope (FIG. 3A, B), La is a uniform, very finely to finely granular dolomite dominated by sub-idiomorphic crystals with a little calcite, either interstitial or as occasional oval patches (?pellets). Organic matter is very variable in amount and is represented by irregular but otherwise parallel streaks of translucent golden yellow to brown amorphous material or opaque debris. There are low but variable amounts of quartz silt and, normally associated with any opaque organic matter, a little framboidal pyrite. Mineralogical analysis (Table 2) shows that the dolomite mineral is ferroan, possibly including the variety ankerite, and reveals the presence of a small proportion of clay minerals. In the British stratigraphical succession, dolomites of this character are restricted to the lithologically varied Kimmeridge Clay Formation (Upper Jurassic), chiefly exposed on the Channel coast of Dorset to the east of Weymouth and in the south-western Isle of Purbeck where, as thin, hard, cementstone bands among predominant mudrocks, they create numerous conspicuous ledges (e.g. Flats Stone Band, Yellow Ledge Stone Band).7 The thin-section appearance of a representative sample from Kimmeridge Bay (British National Grid Reference SY 90 78) is shown in FIG. 3C and the mineralogical composition listed in Table 2.

TABLE 2. MINERALOGICAL COMPOSITION OF REPRESENTATIVE La TESSERAE/OPUS SECTILE/RAW MATERIAL FROM EARLY ROMAN SITES.

weight percentage of crystalline component Site cristobalite quartz mica kaolinite calcite dolomite' Insula IX, Silchester - 8 2 5 3 82

14 2 5 2 77 Kimmeridge - 5 - 3 8 84

Clay Formation, Kimmeridge Bay

Museum of Reading - 6 - 3 1 90 Exeter 13 - 2 - 85 Fishbourne Roman - 7 - 2 1 90

Palace Eccles villa - 7 1 3 3 86 London

Plantation Place tr 6 - 1 tr 93 Plantation Place tr 5 - 2 1 92 Winchester Palace - 7 - 3 1 89 Winchester Palace - 10 - 5 3 82

Caerleon tr 6 - 2 - 92 Norden, Corfe Castle tr 6 - 3 3 88

tr 7 - 4 7 82

'The dolomite mineral is ferroan and may include the variety ankerite.

7 Arkell 1947; Feistner 1989; House 1993; Macquaker and Gawthorpe 1993; Gallois 1998; Morgans-Bell et al. 2001.


The tesserae of La from Insula IX seem to have been manufactured in modular form with the intention of being used directly in this way or after on-site reduction as need dictated. A sub-sample of 518 undamaged/unweathered examples ranged in dry weight - the most convenient measure of size - over two orders of magnitude, from a fraction of a gram to more than 20 g (FIG. 2A). The typical tesserae from the insula may be taken as defining the module, namely, a cuboidal object measuring 9 or 10 mm along each side. Given a bulk density for the rock measured at c. 2470 kg/m3, the modular tessera will weigh c. 1.8-2.5 g. Some of the tesserae have the form of a double cube (double-tessera) and there are a few, neatly fashioned lumps of La that are tabular and resemble four cuboidal tesserae arranged in a square (quadruple-tessera). Descending on the scale of size, there are numerous half-modular tesserae (half-tesserae), shaped as either square tablets or triangular prisms. These could have been produced by dividing a modular tessera along either a perpendicular or a diagonal. Quarter-tesserae are pencil-like and appear to have been made by carefully halving along a perpendicular a half-modular tablet. The gaps between the respective weight ranges as depicted in FIG. 2A arise because, as is to be expected, the cuboidal tesserae as a whole are more variable than is implied by the specification given for the 'typical' modular form.

I I I I

50 quarter- half double- quadruple- A tesserae tesserae tessera tessera

tessera 40tesser essera

no. %

30

20 n 518

10

0 0-25

0"50 100 2.00

4"00 8"00 16-00 32-00 64-00

weight (g)

50 B

40 no. %

30 n=128

20

10

0-125 0-25 0-50 I 00 2-00 4-00 weight (g)

FIG. 2. Size-frequency distributions (weight, logarithmic scales) of undamaged/unweathered tesserae from Insula IX, Silchester. A: lithology La (dolomite cementstone). B: lithology Mc (red burnt mudrock).


Only a small number of tesserae represent lithology Lb, and these include a fragment from a mosaic composed of seven modular tesserae of the rock mortared together. The lithology is a hard, white to very pale cream chalk generally lacking visible shell fragments. Their provenance is clearly in the Upper Cretaceous Chalk, outcropping in England from the English Channel coast to the Yorkshire Wolds, but no attempt has been made to assign them, either lithologically or palaeontologically, to a locality or horizon within that thick and extensive formation.

Lithology Lc is as distinctive as it is rare. It is a yellowish green limestone composed of the shells of small bivalves, ostracods, and smooth-whorled gastropods set in a coarsely crystalline calcite cement. Partly filling the interiors of some shells and other interstices are yellow to dull green, finely crystalline clay-like minerals, probably authigenic. The rock is represented by two small, cuboidal tesserae measuring c. 6 mm along the side. That a Mesozoic-Tertiary source is likely is as much as can at present be said.

Lithology Ld is represented by a single modular tessera. It is a hard, light grey, microcrystalline limestone, but neither a chalk nor a typical marble. The provenance is unknown.

BURNT MUDROCK TESSERAE

The third commonest material (3.21 per cent) in the collections from Insula IX is lithology Ma. In hand-specimen and thin-section (FIG. 5A) it is a very hard to brittle, pale to bright yellow, very fine-grained, fissile shale with a little mica and quartz silt, either scattered fairly evenly through the groundmass or gathered into faint, irregular laminae. Several tesserae have small bivalves and gastropods in mouldic preservation. Typically, Ma is represented by small tablet-shaped or pencil- like tesserae weighing about one gram or less. Given the evidence relating to lithology Mc (see below), the hardness of the material, and the presence of fossils only as moulds, lithology Ma is attributed to the burning of a mudstone of marine origin under controlled conditions.

Lithology Mb in hand-specimen and thin-section is a dull orange to pinkish orange, very hard, faintly laminated mudstone or shale with occasional fossil moulds marked by yellowish streaks. Mb is also represented chiefly by small tesserae. It is finer grained than Mc, into which it appears to grade, and is attributed to burning, as explained below.

The most prevalent burnt mudrock is lithology Mc. In hand-specimen and thin-section (FIG. 5B) this is seen to be a bright to dark red, very hard to brittle, uniformly-textured to 'streaky' or well laminated, silty mudstone to shale generally with fossil moulds marked by a yellow selvage. On weathering, the rock becomes dusky pink, either in a surface rind or throughout. A sub-sample of 128 of the tesserae considered to be undamaged gave a narrow, smoothly unimodal distribution of weights (FIG. 2B) quite different from that of the carbonate rock La (FIG. 2A). The tesserae of Mc vary from small cuboidal forms with sides measuring 5-7 mm to tablet- and pencil-like shapes and some resembling a triangular prism. Several preserve the moulds of molluscs and one of the largest, examined in detail (see Palaeontological Note below), has an assemblage compatible with a Jurassic age.

The colour, hard and brittle character, and presence of fossil moulds is consistent with Mc having originated in the burning of an originally organic-rich silty shale of marine origin to temperatures in excess of c. 6500C, either deliberately or during the course of a wildfire. The geological literature shows that shales belonging to the Lias and the Kimmeridge Clay Formation of Jurassic age exposed along the Dorset coast have been set on fire in many places for short periods (e.g. Burning Cliff). Although spontaneous combustion has been claimed, in most cases a lightning strike was probably responsible, and in certain instances the burning was deliberate and controlled, for example, during post-medieval attempts to work the Kimmeridge Clay Formation for oil-shale.8 Of an example of

8 e.g. Buckland and De la Beche 1835; Cole 1974.


the combustion of the Kimmeridge Clay Formation in Ringstead Bay, Dorset, Buckland and De la Beche write that 'much of the shale near the central parts [of the fire] has undergone a perfect fusion, and is converted to a cellular slag. In the parts adjacent to the ignited portion of the cliff, where the effect of the fire has been less intense, the shale is simply baked and reduced to the condition of red tiles'.9 Similar reddened shales can be found at the sites of oil-shale works (e.g. Kimmeridge Bay), and waste from these sites, in hand-specimen and thin-section, is a close match for Mb and Mc. We also note that the unusual 'streaky' microscopic structure depicted in FIG. 5B has parallels in some mudrocks of the Kimmeridge Clay Formation.10 Given these and other observations, and in the further light of the evidence of fossils above and to be presented from another early Roman mosaic site (see below), it accordingly seems probable that Mc and Mb are from the beds in Dorset. Ma could also derive from the Kimmeridge Clay Formation, but from a finer-grained and possibly slightly calcareous facies burnt under less oxidising conditions. Yellow burnt mudrocks, however, have not so far been recorded from the Dorset coast.

CERAMIC TESSERAE

The commonest ceramic tesserae - small compared to the modular form of La - are chiefly cuboidal forms in fabric Ca. They are made of a hard to very hard, sandy ceramic material that grades outward in colour from dark red, through dark reddish grey, to purplish black beneath a flat surface with a thin, slightly vesicular, vitreous coating. The ceramic could have come from an overfired pot or tile but most resembles clay furnace-lining.

Fabric Cb is clearly pottery. It is orange, grading outward to yellowish brown, soft, porous, and sandy. The tesserae are again small.

Possibly from brick or tile, fabric Cc is red, moderately soft, and composed of a silty groundmass tempered with plentiful quartz sand and grains of flint. These tesserae are also small. Given the temper, this fabric is probably local to Silchester.

Fabric Cd is also pottery. It is a soft, porous ceramic grading outward from pale yellow-orange to orange, and is composed of scattered, well sorted quartz sand and clay pellets with a little grog set in a coarsely micaceous groundmass. Only one small tessera is known.

A South Gaulish samian vessel afforded the single tessera representing fabric Ce. It is hard, reddish orange in colour, and extremely fine-grained, with occasional tiny white inclusions.

Another pottery fabric was used to make two small tesserae. Fabric Cf is soft, orange, and composed of abundant clay pellets and ore set with scattered medium-grained quartz sand in a slightly micaceous groundmass.

Fabric Cg is soft, orange, and formed of a slightly micaceous, very fine-grained ceramic with occasional very coarse-grained quartz sand. The tessera is small.

OTHER TESSERAE

The excavations yielded several small flint tesserae. They are sub-cuboidal in form, due to the shape and natural fracturing of the parent material, and are water-worn. Lithology Fa is brownish grey and seems to have developed in the Chalk mainly as thin plates. Lithology Fb is a dull reddish brown due to burning.

There are a few tesserae of two miscellaneous categories. The tesserae of lithology Xa are greyish brown, soft and earthy, but of uncertain composition. The lithology may be a severely weathered form of the dolomite La. Category Xb, represented by small tesserae, is a dark blue, opaque, slightly vesicular glass or fuel-ash slag.

9 Buckland and De la Beche 1835, 23; see also House 1993, 115. 10 Macquaker and Gawthorpe 1993.


SILCHESTER MOSAICS AT THE MUSEUM OF READING

Of the floors recovered from the early excavations of Joyce and the Society of Antiquaries, an outstanding example of a probably early floor was lifted in 1898 from the remains of a house underlying House 2 in Insula XIX (Mosaic 2, Museum of Reading)." Traces of robbed outer (masonry) walls were identified, as well as of possible timber partitions between internal rooms. The building was put forward by the excavators as the first example of a half-timbered construction at Silchester. Although no dating evidence was recovered, the house shares the same orientation as the Roman street grid and is therefore likely to be later than it, that is, later than about the mid-first century A.D. Although we cannot be certain without further excavation, on the basis of the dating of the sequence of buildings on the site of 'House' 1 in Insula IX,12 the structure beneath House 2 in Insula XIX was probably erected in the later first century A.D. and demolished before the mid-third century.

Although Mosaic 2 is badly damaged, two borders remain reasonably well preserved, and there are fragments of a further border and of the centre of the pavement.13 One panel, almost complete, depicts in black against a white background tendrils and leaves of the acanthus Smilax aspera along its length. The border of the adjoining square has a scroll in a variety of colours - reds, yellows, greys and blacks - against a white background. Of the central part, divided into small rectangular panels, only parts of the guilloche and traces of fine figured work, depicted in red, yellow, grey, white, and black, survive with any integrity. The excavators14 described the black material as a 'sandy limestone', the white lithology as 'hard chalk', the two shades of red as of 'brick', and the pale yellow materials as 'perhaps also brick'. The greenish-grey stone they identified as 'Purbeck marble'.

Parallels, at least in terms of the polychrome materials used, are to be found with the panels of a second floor, inserted into a framework of coarser materials. It was discovered in 1895 decorating the floor of a long room or corridor on a broadly east-west line that linked the east and west ranges of House 2 in Insula XIV (Mosaic 1, Museum of Reading), but in House I (Room 23) in the same insula a well-preserved and purely bichrome (black-and-white) mosaic was encountered.15 Although apparently earlier than the eastern range, which appears to have been built around it, there is no independent evidence for the date of the corridor in House 2 or of the other constituent parts of the house. However, it is at right-angles to the western half of the building, which shares an orientation a few degrees at odds with that of the street grid. Hence this element of the house may be relatively early, of later first- or second-century A.D. date. The excavators observed that one of the panels of Mosaic 1 was decorated in the form of a basket of flowers and used tesserae of 'glass paste'.16 Aside from this specific case, and a reference to the bright red tesserae as 'always of brick', there is little comment on the materials used for the flooring in the corridor. They were, however, considered to be the same as those used for a number of mosaics in House 1 in the insula, and to be largely 'of native stones'. The bichrome mosaic from House I has an over-all fret or key pattern alternating with squares filled with simple geometric motifs, of at least twelve kinds. This floor has stylistic similarities with a mosaic in Room N 13 at Fishbourne Roman Palace (see below).

Mosaic 2 from House 1 in Insula XIX at Silchester is now stored at the Museum of Reading, where it was examined. Although the surface was not clean, sufficient was clearly visible to confirm that the

11 St John Hope and Fox 1899, plans, esp. facing p. 244; Boon 1974, 217-21; we are indebted to Jill Greenaway for the opportunity to examine the Silchester mosaics preserved at the Museum of Reading.

12 Clarke and Fulford 2002. 13 St John Hope and Fox 1899. 14 St John Hope and Fox 1899, 249. 15 St John Hope and Fox 1896, plan facing p. 234, 241-2, pl. XIII; Boon 1974, 215-17. 16 St John Hope and Fox 1896, 242-2, 246.


constituent materials were a hard, white chalk, a subordinate dark grey-black stone, and an occasional dark red material, as well as a range of ceramics. The grey-black material is a cementstone, the cleaner, lighter-weathered tesserae of the rock revealing abundant parallel streaks of black organic matter. This lithology and the chalk are represented chiefly by tablet-shaped half-tesserae set parallel with the surface of the mosaic in a white mortar. Many of the tesserae are large (c. 15 by 15 by 6-9 mm)- as the excavators noted - compared to their counterparts from Insula IX (FIG. 2A).17 The excavators commented, however, on the frequency with which tesserae one-quarter of an inch square (c. 6 by 6 mm) or smaller were used, remarking, 'No other pavement as yet found on the site has shown such delicate work as is here exhibited'. The dark red material occurs only as small tesserae and, at least under the hand-lens, is not brick but identical in our judgement to lithology Mc at that site. We are unable to confirm the presence of Purbeck marble reported by the excavators.

A cementstone tessera loosened when the mosaic was moved to the store proved to be a ferroan dolomite with a little quartz and kaolinite (Table 2). Another, in thin-section (FIG. 3D), is a finely granular dolomite with a small but varying amount of yellow to brown, amorphous organic matter in irregular streaks, a little opaque organic material with pyrite, and scattered quartz silt. On this basis, the dark grey stone in Mosaic 2 - the 'sandy limestone' of the excavators - may be confidently identified as lithology La at Insula IX (FIG. 3A, B; Table 2), which we consider to have been procured from the Kimmeridge Clay Formation (FIG. 3C, Table 2).

Mosaic 1 from House 2 in Insula XIV is represented by fragments of guilloche from one of the small panels. Hand-lens inspection reveals tesserae of white chalk, Kimmeridgian cementstone, and an orange ceramic set in a white mortar. As these were all in situ, petrographic and mineralogical analyses were not attempted.

The bichrome mosaic from House 1 in Insula XIV can be seen on the wall of the Atrium Gallery at the Museum of Reading. The exposed surfaces of the tesserae are scratched, pitted, weathered, and in many cases stained. However, hand-lens inspection showed the white stone to be from the Chalk, and the grey-black material to be a finely granular cementstone resembling that in the other Silchester mosaics that had been examined. The better preserved of the 'black' tesserae were finely streaked with dark organic matter.

SOME OTHER EARLY MOSAICS IN SOUTHERN BRITAIN

INTRODUCTION

The preceding sections have established the material relationship between the loose tesserae from Insula IX at Silchester and the mosaics from Insulae XIV and XIX. In the case of the latter, there is a strong a priori case for an early date, such that we can reasonably add it to the schedule of the earliest mosaics from Roman Britain. For Insula XIV, further excavation is required to test the hypothesis. Since the same geological materials were used in mosaics across three scattered insulae, the probability is that they were used extensively across the town.

To turn for confirmation of the earliest use of our materials we need to explore those sites where there are survivals of mosaics, or at least of mosaic and other fine flooring materials, combined with good dating evidence. This combination we find with confidence at three sites: the 'proto-palace' phase of the villa at Fishbourne (West Sussex), the Neronian legionary fortress at Exeter, and certain sites in London. Although the excavations are not yet fully published, the case for an early date for mosaics at the Eccles villa (Kent) is strong, and there is plausible inferential evidence to add material from the early-founded villa at Angmering (West Sussex) to the list. Caerleon, fortress of Legion II Augusta after Exeter, along with the 'palatial' phase at Fishbourne, and further finds from London,

17 St John Hope and Fox 1899, 249.


FIG. 3. Dolomite cementstone tesserae (x10). A: Insula IX, Silchester; B: Insula IX, Silchester; C: Kimmeridge Clay Formation, Kimmeridge Bay; D: Silchester Mosaic 2, Museum of Reading; E: Legionary bath-house, Exeter; F: Fishbourne

Roman Palace.


FIG. 4. Dolomite cementstone tesserae and opus sectile (xl0). A: Eccles villa; B: Angmering villa; C: London, Watling Court; D: London, Winchester Palace; E: Fortress bath-house, Caerleon; F: Norden, Corfe Castle.


FIG. 5. Burnt mudrock tesserae and raw material (xl0). A: Ma, Insula IX, Silchester; B: Mc, Insula IX, Silchester; C: Ma, Fishbourne Roman Palace; D: Raw Mc, Fishbourne Roman Palace; E: Mc, opus sectile, Angmering; F: Mc, Caerleon.


provide evidence for the continued use of our materials into the late first/early second century A.D. The Silchester floors probably belong to this stage. For evidence from this time of the primary working of raw material into tesserae and opus sectile we turn to the site of Norden, Corfe Castle (Dorset).

EXETER (DEVON)

The fortress of Legion II Augusta was established at Exeter (FIG. 1) in c. A.D. 55.18 Some twelve fragments of mosaic and many loose tesserae in a number of colours are believed to have come from a mosaic or mosaics contemporary with the construction of the baths, c. A.D. 60. Three fragments were found in the demolition deposit of c. A.D. 75, the remainder in that of c. A.D. 80.19 Apart from the largest fragment (140 by 155 mm), which appears to depict a disc confronted by hoofed creatures, perhaps a globe flanked by Capricorn and Pegasus, as emblems of Legion II, little can be said about what was originally portrayed.

These fragments of mosaic and loose tesserae were subjected to hand-lens examination at the Royal Albert Memorial Museum and Art Gallery.20 Opus signinum had been used to bind the tesserae, and only three colours are represented.21 We concur that the small red tesserae preserved in three fragments were manufactured from samian sherds, and that the white tesserae, described as a 'fine-grained limestone, possibly from the Beer quarries near Lyme Regis', are of a hard chalk. The 'blue-grey' tesserae were described as 'of calcium iron carbonate or siderite of uncertain origin'.

This 'ferruginous' rock is represented chiefly by modular tesserae, but with some double-tesserae, half-tesserae of triangular section, and occasional tablet-shaped half-tesserae set on edge. The modular tesserae (c. 1.5 g) are on the small side compared to Insula IX at Silchester (FIG. 2A). The rock is dark brownish grey weathering to pale grey, weakly effervescent, finely granular and, on surfaces that cut the bedding, finely streaked with dark organic matter. Mineralogical analysis reveals a ferroan dolomite with subordinate quartz and a little clay (Table 2). Representative thin-sections of other tesserae (FIG. 3E) confirm the predominance of dolomite and show a faintly laminated rock with small amounts of yellow-brown amorphous and opaque organic matter in parallel streaks and very occasional quartz silt. There is occasional pyrite and one preparation included a fish scale. The ferruginous blue-grey tesserae from the bath-house at Exeter are identical in all essential respects with lithology La at Silchester (FIG. 3A, B; Table 2) and we consider them to have been procured from the Kimmeridge Clay Formation of Dorset (FIG. 3C, Table 2).

FISHBOURNE ROMAN PALACE (WEST SUSSEX)

The earliest evidence of surviving mosaics from the great Roman building at Fishbourne, at the head of Chichester Harbour (FIG. 1), comes from the Flavian 'palace' of Period II, dating from c. A.D. 75.22 They are now protected, along with floorings from Period III, within a covered space over the North Wing. Most of the mosaics available for inspection are in black and white, presenting a limited range of patterns: squares within a framework of diagonal lines forming lozenge shapes; squares set alternately with swastika-meander shapes; repetitive overlapping rectangles; and a chequerboard of solid squares of two different sizes. The motifs include compass-designed rosettes, rosettes of leaves and scrolls, triangles placed apex to base, squares set diagonally within squares, squares overlapping a central square, and infilled crosses. Although the preservation is fragmentary, the motifs seen in a mosaic from Room N13 invite comparison with those of the bichrome mosaic from House 1 in Insula XIV at Silchester. The squares are larger than at Silchester, however, and the motifs they

18 Bidwell 1979. 19 Smith 1979. 20 John Allan kindly facilitated this opportunity. 21 Smith 1979, 132-4, pl. XVI. 22 Cunliffe 1971a, 58, 59, 97, 146-50, pls 23b, 80c; 1971 b, 16, 41-2.


contain appear to have been more complex. The polychrome mosaic in Room N20 is of a highly advanced design, composed of a circular panel enclosed within a square, with motifs incorporating tendrils extending into the corners. The chief material in these mosaics was briefly described as a 'hard white chalk', ascribed to the local Upper Chalk (?Chalk Rock). Also reported as tesserae was 'a grey sandy shale ... similar to stones of the Wealden series of East Sussex', later described as a 'dark grey ... hard silty shale', and claimed, but without supporting evidence, to be 'from a Jurassic, possibly Kimmeridge, shale'.

Altogether we examined four groups of material from Fishbourne: the earliest a block of raw stone from the Neronian-early Flavian builders' yard; in situ or relocated mosaic floors of Period II and Period III date in the North Wing (hand-lens inspection only); and loose tesserae from later excavations of the west wing and from an area to the east of the Period II 'palace'.23 The covered floors are clean and uncoated, allowing identifications to be made with some confidence. In most cases the full extent of the mosaic was accessible.

Tesserae of hard white chalk dominated all the floorings. The tesserae for the decorative elements are predominantly of a brownish grey, weakly effervescent, finely granular cementstone weathering from mid-grey to dark grey and, in a few cases, to almost black. Tellingly, the paler surfaces carry fine streaks of dark organic matter, and we accordingly identify the stone as lithology La at Silchester, which we show was procured from the Kimmeridge Clay Formation. The earlier mosaics, in Rooms N3, N424 and N12,25 are of chalk and cementstone only. Some coloured tesserae appear in the slightly later mosaics. The 'Fortress' mosaic relaid in Room N16,26 but originally beneath the 'Dolphin' mosaic in Room N7, has some tesserae of orange-red ceramic and a few, in the corners, of a pale grey limestone-sandy limestone. The 'Dolphin' mosaic in Room N727 includes ceramic tesserae, bright red in some cases but dark red to blackish red and hard-fired in others. There are also tesserae of yellow-orange fine-grained limestone. Two superimposed floorings with some coloured tesserae are visible in Room N13. The lower28 includes a reddish black, very fine-grained limestone. The upper29 also has this limestone, accompanied by a pale yellow to white very fine-grained limestone or possibly chalk, a bright red ceramic, a reddish black ceramic, and a hard, dusky pink burnt mudrock comparable with lithology Mc at Silchester. The coloured tesserae seen in Room N2030 are a buff and a red ceramic, accompanied by a bright yellow burnt mudrock with scattered shell fragments preserved as moulds. The latter under the hand-lens is indistinguishable from lithology Ma at Silchester. These various hand-lens identifications are borne out by petrographic and mineralogical work on similar loose material at Fishbourne.

The typical loose cementstone tessera from the area of the palace is cuboidal but slightly larger (c. 11 by 11 by 11 mm) than its modular counterpart at Insula IX, Silchester. A sample of fourteen of these tesserae ranged in weight from 1.61-6.70 g, averaging 3.35 g (cf. FIG. 2A). Mineralogically, the rock is a ferroan dolomite with a little quartz and occasional calcite and kaolinite (Table 2). Thin- sections show a finely granular dolomite with variable amounts of yellow-blood red, amorphous organic matter and opaque organic material with pyrite in fine, irregular, parallel streaks (FIG. 3F). There is some quartz silt and very occasional fish bones and scales. The material compares well with cementstones in the Kimmeridge Clay Formation (FIG. 3C).

The later excavations also afforded many small to large tesserae of a dusky pink to dark red

23 We are indebted to David Rudkin for this opportunity. 24 Cunliffe 1971a, 94, pl. 21 (Period II). 25 Cunliffe 1971a, 96-7, pls 24, 58 (Period II). 26 Rudkin 1981, fig. 5. 27 Cunliffe 1971a, 163-5, pls 47-53, 83, 88 (Period III); dated after c. A.D. 160 by Rudkin 1981, 8. 28 Cunliffe 1971a, 97, pls 23b, 80c (Period II). 29 Cunliffe 1971a 158-9, pls 43-4 (Period III). 30 Cunliffe 1971a, 99, 149, pls 26-7, 81, 91 (Period II). Ling (1997, 270) questions this date.


material, and a lesser number of a bright yellow lithology. The latter in thin-section (FIG. 5C) is a very fine-grained shale with little or no quartz silt except as occasional coarse laminae or burrow- fills. It is indistinguishable from the burnt mudrock Ma at Silchester. The pink-red material in hand- specimen and thin-section is the same as lithology Mc at that site. It is a hard, brittle, crudely fissile, silty mudstone with occasional fossil moulds marked by yellowish selvages.

Much worked stone was recovered from an area interpreted as a builders' working yard beneath the East Wing of the Flavian palace and contemporary with the Neronian-early Flavian 'proto-palace'.31 Found in large amounts was a 'red fossiliferous silty mudstone' of 'probably Mediterranean origin' and, in lesser quantity, a 'buff-coloured [later described as yellow] fossiliferous silty mudstone, probably of similar origin'. These materials had been used at the yard to produce opus sectile tiles -

square, triangular, diamond-shaped and kite-shaped in the case of the red, and kite-shaped in the case of the single example in yellow. We were able to examine a substantial lump of raw material of the red lithology probably from the yard. It is identical with lithology Mc at Silchester, which we regard as burnt mudrock from the Kimmeridge Clay Formation. The rock is a dark red, pink-weathering, crudely fissile, 'streaky' to faintly laminated, silty mudstone with fossil moulds marked by yellow selvages (FIG. 5D). This richly fossiliferous lump (see Palaeontological Note below) contains a perisphinctid ammonite of the genus Pectinatites, restricted to the upper part of the Kimmeridge Clay Formation (Jurassic, Lower Volgian Stage). A recent study asserts the same provenance for the red burnt mudrock, but offers no supporting evidence.32 We have not been able to examine the yellow opus sectile, but the published description strongly suggests lithology Ma, known as tesserae in the Flavian mosaics and as loose material.

Fairly common at the yard is 'a grey sandy shale', later reported as 'grey-brown siltstone' or 'grey Wealden shale',33 but also as a possible Kimmeridge shale, in the light of then recent discoveries at Corfe Castle (see below).34 It was used for a small range of geometrical tiles and, in the Flavian palace, as wall-inlay along with the red and yellow burnt mudrocks. We have not seen the tile or inlay of grey siltstone but, in the form of tesserae, the same name is applied to our lithology La at Silchester, procured from the Kimmeridge Clay Formation and therefore not from Wealden rocks or the Weald.

ECCLES VILLA (KENT)

The village of Eccles overlooks the valley of the tidal Medway c. 6 km to the north-north-west of Maidstone (FIG. 1). The earliest Roman phase (Period I) of the villa there, excavated over many years (1962-76), has been dated to c. A.D. 65. While interim reports, including a summary report of the whole, have been published, the full report, with detailed chronological evidence, is still awaited.35 The mosaic fragments in question here were derived from Room 46, but are assumed to have been stripped from the frigidarium of the Period I bath-house, which was destroyed c. A.D. 120. The excavator considered that the original mosaics had been salvaged and stored for re-use. Although doubts have been expressed about a date as early as c. A.D. 65 for these mosaics, that possibility still remains. Greater confidence may be attached to the date of c. A.D. 120 as a terminus ante quem. Most of the fragments have lozenge patterns while others have flower motifs, simple and three-strand guilloche, and parts of what may be human figures. The latter are cogently argued to be the remains of two gladiators.36 Previous descriptions of the mosaic materials referred only to their colours of white, yellow, orange, green, blue-grey, red-purple, and shades of black.

31 Cunliffel971a, 58; 1971b, 16, 33-5. 32 Peacock and Williams 1995. 33 Cunliffe 1971b, table 4. 34 Cunliffe 1971b, 16, 41. 35 Detsicas 1963, 1964, 1965, 1969, 1977. For general background see Detsicas 1987. 36 Neal 1981, 76 (Mosaic 43).


Hand-lens inspection showed Mosaic 1 from the frigidarium to be made of at least four different geological materials, set in a white, sandy mortar: hard white chalk, very pale grey limestone, a dark red lithology, and dark grey cementstone.37 There are also some ceramic tesserae. The limestone is a compact rock formed of well sorted and rounded, coarse-grained biogenic fragments with scattered, ovoidal pellets of greenish black glauconite cemented by coarsely crystalline calcite. A local Lower Cretaceous source seems likely, given the presence of glauconite. The dark red material is a hard, brittle, faintly laminated, burnt mudrock with scattered fossil moulds marked by yellow selvages. It occurs as small, cuboidal tesserae and is indistinguishable from Mc at Insula IX, Silchester. The dark grey cementstone is coarsely granular, weakly effervescent and marked by abundant, parallel streaks of black organic matter. It closely resembles lithology La at Silchester and occurs as mainly modular tesserae, but on the small side compared to that locality.

Mosaic 3 was composed of tablet-shaped, half-tesserae of hard chalk and dark grey cementstone, both laid parallel with the surface, together with some small, mainly cuboidal tesserae of dark red and yellow burnt mudrocks, and orange, red and buff ceramics. The mortar is again sandy and white. A cementstone tessera prepared in thin-section (FIG. 4A) is a faintly laminated, finely granular dolomite with very abundant irregular but parallel streaks of blood-red, amorphous organic material, scattered circular-ovoidal areas of microcrystalline calcite (?pellets) and some opaque organic matter with pyrite. Table 2 gives the mineralogy of another tessera. Although the thin-sectioned example is not wholly typical, the grey cementstone is clearly the ferroan dolomite lithology La at Silchester (FIG. 3A, B), from the Kimmeridge Clay Formation (FIG. 3C, Table 2). The half-tesserae (weight c. 0.7-0.9 g) are, however, on the small side compared to those from the town (FIG. 2A). A thin-sectioned red tessera showed a dense, crudely laminated, silty mudrock with scattered fossil moulds, similar to lithology Mc at Silchester. Resembling in thin-section lithology Ma at Silchester was a yellow tessera. The material is a faintly laminated, very fine-grained shale with fossil moulds and, exceptionally, a band of mixed quartz silt, clay, and dolomite crystals. The dolomite suggests a source linked stratigraphically with that of Mc.

ANGMERING VILLA (WEST SUSSEX)

The remains of the Roman villa at Angmering lie c. 24 km to the east of Fishbourne (FIG. 1).38 Although only the bath-house has been excavated, the evidence for the quality of the interior decor has been seen to parallel the furnishings of Fishbourne in its proto-palace phase, and there is a precise parallel in the surviving opus sectile.39 Indeed, it was suggested that the two buildings were by the same architect.40 Although the chronological evidence is limited, it supports a possible Neronian- early Flavian date of c. A.D. 65-75.

A considerable range of flooring and building materials was reported from Angmering.41 The opus sectile, represented by triangular, trapezoidal, kite-shaped, square and octagonal tiles, is said to be of 'pink, yellow and dark grey stones from the Wealden series, white limestone from northern Italy, together with Sussex marble'. An implicit reference to the presence of a bichrome mosaic hints at the use of 'grey stones obtained from the Weald near-by'. Geological examination of some of the building materials suggested the presence of the local Upper Chalk (building blocks),42 a coarsely crystalline white marble (a slab), and the foraminiferal Scaglia limestone of northern Italy (white tesserae and tiles).43

37 We are indebted to David Neal for the opportunity to examine and sample this material. 38 Scott 1938, 1939; Wilson 1947. For general background see Cunliffe 1973. 39 Cunliffe 1971b, fig. 17 (bottom left). 40 Cunliffe 1971a, 63, 65, 67, 75. 41 Scott 1938, 15, 17. 42 Scott 1938, 43 (reported by E.C. Martin). 43 Scott 1938, 43-4 (reported by K.P. Oakley).


As at Eccles, the flooring of the bath-house was not encountered in situ. Some of the excavated material - fragments of mosaic and loose tesserae and tiles - is retained in the Educational Collection at the Littlehampton Museum, where it was subjected to hand-lens examination.44 The number of mosaic floors represented is uncertain but the character of the tesserae we have seen suggests that there was more than one.

The collection includes two fragments of a mosaic composed of small, cuboidal to tablet-shaped tesserae (c. 11 by 8 by 5 mm) of a white, compact, very fine-grained, marble-like limestone, which may be the same as the rock claimed to be the Scaglia limestone. One fragment is wholly of this lithology, whereas in the other there are a few tesserae of a dark grey to black stone. This differs significantly from lithology La at Silchester, being non-effervescent and without visible streaks of organic matter. The tesserae are set in white mortar with a little sand and occasional crushed brick/ tile.

The other mosaic fragments and loose tesserae are more familiar. A hard, white chalk is represented by loose tesserae and by a small cluster of medium-large, cuboidal forms. The other rock present is grey-weathering, weakly effervescent, finely granular and streaked with dark organic matter. It is represented chiefly by a group of large double tesserae (c. 12 by 13 by 23 mm) set vertically in opus signinum. A loose tessera was thin-sectioned (FIG. 4B), revealing a faintly laminated, finely granular dolomite with a small to moderate amount of yellow-reddish brown, amorphous organic matter in irregular streaks, accompanied by two fish bones/scales. There was insufficient material for mineralogical analysis in addition, but there can be little doubt that the rock is the same as lithology La at Silchester (FIG. 3A, B), namely, a cementstone from the Kimmeridge Clay Formation (FIG. 3C).

Only pink floor tiles had been retained. Edges and a representative thin-section (FIG. 5E) reveal a hard, pink-weathering, dark red, streaky to crudely laminated, silty mudstone with numerous moulds of shell fragments and occasionally of large bivalve molluscs, all marked by yellow selvages. The material is indistinguishable microscopically and in hand-specimen from lithology Mc at Silchester and elsewhere. The presence of red burnt mudrock suggests that the yellow tiles at the bath-house are of lithology Ma, and that the grey stone reported as opus sectile is the Kimmeridgian cementstone (FIG. 3C). The claimed procurement of the 'pink, yellow and dark grey stones from the Wealden series',45 or from the Weald, can no longer be sustained.

LONDON

We examined samples of loose tesserae from three different locations in London, two from north of the Thames, east and west of the Walbrook, and one from Southwark to the south (FIG. 1).46

The tesserae from mosaic fragments excavated at Watling Court, west of the Walbrook, were associated with timber-framed Buildings D, F, and H of Period 4, assigned a Flavian-Trajanic date. These buildings were destroyed by the Hadrianic fire of c. A.D. 120-130. Although we cannot attribute our tesserae to particular mosaic fragments, the predominant colours of them all are black and white.47 The loose material includes both modular and double-tesserae. The white material is a hard chalk but the black is a fine-grained, yellowish brown, weakly effervescent cementstone marked by fine, parallel streaks of dark organic matter. In thin-section (FIG. 4C) the rock is a finely granular dolomite with variable amounts of yellow to brown, amorphous organic material in sub-parallel streaks, opaque organic matter, and occasional quartz silt and pyrite. The tesserae had been mounted in white, sandy mortar with occasional crushed brick/tile.

44 Rebecca Fardell kindly arranged for us to examine what has survived from the excavations. 45 Scott 1938, 15, 17. 46 These observations were made possible through the kindness of Jennifer Hall, Susan Pringle, and John Shepherd. 47 Perring and Roskams with Allen 1991, esp. 88-94, with a note on the pavements by D.J. Smith, 88-94.


Excavations in 2000 to the east of the Roman forum at Plantation Place, Fenchurch Street, produced evidence of timber-framed buildings dating from c. A.D. 70.48 One of these, also destroyed by the Hadrianic fire, was decorated with mosaic floors in adjacent rooms. The numerous loose tesserae we examined from the two, differently dated, contexts at this site are of a brownish grey weathering to pale grey, weakly to moderately effervescent cementstone marked by fine, parallel streaks of dark organic matter. In a few cases with traces of white mortar, they are chiefly modular tesserae similar in size to those at Silchester (FIG. 2A), but there are some double-tesserae. Mineralogical analysis (Table 2) showed predominant dolomite with some quartz and small or trace amounts of kaolinite, calcite, and cristobalite. Microscopically, the rock is a finely granular dolomite with occasional to abundant, sub-parallel streaks of mainly brown, amorphous organic matter, scattered quartz silt and some pyrite. Occasional fish bones/scales were noted.

From south of the Thames we examined loose tesserae from the Winchester Palace excavation. These appear to be from Building 13, Room B, where the mosaic has a guilloche-mat design dated after c. A.D. 120.49 They are chiefly double-tesserae and some modular tesserae, similar in size to those at Silchester (FIG. 2A), of a yellowish to brownish grey, weakly effervescent, cementstone finely streaked with dark organic matter. Mineralogical analysis (Table 2) revealed predominant dolomite with subordinate quartz and some kaolinite and calcite. In thin-section (FIG. 4D), the rock is a finely crystalline dolomite with abundant irregular streaks of golden brown, amorphous organic matter and occasional pyrite framboids and quartz silt. A poorly preserved foraminifera was noted. Representing another, unrelated lithology was a single tessera of dark grey, sandy limestone with scattered grains of greenish-black glauconite.

With Fishbourne in mind, cementstone tesserae from London sites have in the past been uniformly identified as of 'Wealden shale'. The mineralogical and petrographic features we record above, however, clearly proclaim the rock to be the same as lithology La at Silchester, and from the Kimmeridge Clay Formation of Dorset. Indeed, this lithology may be ubiquitous in early Roman floorings in London. Tesserae of 'Wealden shale', presumed to be the rock, together with those of chalk, are extensively recorded from excavations undertaken during 1991-98 in Southwark.so Their contexts range in date from the first century to the early second century A.D. Not only were cementstone tesserae found, but opus sectile tiles of 'Wealden shale' occurred at one site, in a pre- Boudiccan setting (Borough High Street) next to the main road leading south from the river crossing. Lithology Mc at Silchester - the red burnt mudrock - seems also to be present in at least two contexts, being described, again with Fishbourne in mind, as a 'deep pink, shelly, mudstone from a Mediterranean source'. The glauconitic sandy limestone found at Winchester Palace is probably from a comparatively local, early Cretaceous 'greensand' formation.

CAERLEON (GWENT)

In c. A.D. 75 Legion II Augusta was transferred from Exeter or possibly Gloucester to Caerleon in south-east Wales, where a fortress was built on heights overlooking the valley of the tidal Usk (FIG. 1). There the legion remained until the late third century A.D.51

The only in situ mosaic known from the bath-house located within the fortress is represented by the substantial fragments discovered in 1877 at Backhall Street and dated to the A.D. 80s.52 Some of the flooring has survived, especially the substantial fragment portraying a possible thyrsus, an

48 MOLAS site FER97. Although the majority of the tesserae supplied come from contexts with a terminus post quem of A.D. 70, one group derives from a potentially earlier context dated A.D. 50-70. Brigham 2001a, 2001b.

49 We are grateful to Carrie Cowan for this information in advance of publication. 50 Drummond-Murray et al. 2002, 151-61. 51 Brewer 2002; Knight 2003, 8, 13. 52 Zienkiewicz 1986, 165-9, 339-40.


arrangement of ivy leaves inserted into the end of a hollow plant stem, associated with the cult of Bacchus.53 The original mosaic, set in opus signinum, appears to have been square with an outer border of four coloured bands and an inner square of one band which encloses several more, concentrically arranged coloured bands. A wreath lies between the outer bands and the inner square. Five colours of tesserae were used, described as creamy-white, dark grey/black, light bluish grey/blue, yellow, and red. The thyrsus fragment itself is displayed on one wall of the Fortress Baths building, under a modem cover, but poor lighting makes it difficult to examine the constituents with any thoroughness. However, all of the colours described appear to be represented. A few loose tesserae from the Victorian excavations have also been retained. Loose tesserae were also recovered, in substantial numbers, from various contexts during excavations at the baths in 1964-65, 1967, and 1981. These are described as white, grey brown/black, red (a stone not ceramic), and Purbeck marble.54 The white tesserae are identified as chalk and the brown/black as 'an argillaceous mudstone of uncertain origin'.

Mosaic fragments and loose tesserae from the Victorian excavations were examined at the Roman Legionary Museum, and the thyrsus fragment itself was also scrutinised.55 Many of the loose tesserae are of a dark grey fine-grained, weakly effervescent cementstone finely streaked with black organic matter. One included as a mould part of a ribbed fossil, possibly an ammonite. A tessera subjected to mineralogical analysis was composed predominantly of ferroan dolomite with a little quartz, some kaolinite and a trace of christobalite (Table 2). In thin-section (FIG. 4E) the rock is a finely granular dolomite with a small amount of yellow-brown amorphous organic matter, a little opaque organic material with pyrite, and occasional quartz silt, fish bones and scales. It compares closely with the dolomite cementstones in the Kimmeridge Clay Formation (FIG. 3C). Many dolomite cementstone tesserae finely streaked with organic matter occur among the loose material from the excavations of a century later.

Also present at Backhall Street are tesserae of hard, white chalk, dark red burnt mudrock similar to lithology Mc at Silchester, a single tessera in orange ceramic, and tesserae of a pale grey, strongly effervescent, calcareous cementstone, probably from the local Lower Jurassic Lias. The dolomite, red mudrock, and ceramic are also represented among the loose material excavated later at the site of the bath-house. The red mudrock in hand-specimen and thin-section (FIG. 5F) is a streaky to crudely laminated mudstone with abundant quartz silt and occasional fossil moulds marked by yellowish selvages. Also present are a smaller number of tesserae of yellow burnt mudrock closely resembling lithology Ma at Silchester. A thin-section revealed a delicately laminated, very fine-grained shale with occasional quartz silt. Similar assemblages of loose tesserae have come from the Prysg Field Barracks and the canabae.56

As has been noted,57 a striking feature of the fortress tesserae is their frequently large size, a property extending to those of burnt mudrock. Although there are roughly cuboidal tesserae similar to the modular form at Silchester, there are abundant cuboids that are several millimetres larger, especially those of chalk, and numerous double-tesserae, set on end, of dolomite or mudrock that measure 25-35 mm in length. As a whole, the tesserae are much larger than those known from the legion's earlier bath-house at Exeter (see above).

NORDEN, CORFE CASTLE (DORSET)

Excavation at Norden, combined with random finds, has established the presence of a substantial, long-lived Romano-British industrial settlement c. I km to the north and north-west of Corfe Castle

53 Boon 1986. 54 Boon 1986, 273; Zienkiewicz 1986, 342. 55 We are grateful to Richard Brewer and Mark Lewis for this opportunity. 56 Nash-Williams 1931, 1932; Knight 2003, 43-8; Evans 2000. 57 Boon 1986, 273.


in the Isle of Purbeck, south-east Dorset (FIG. 1).58 The economy was based on industrial activities, especially the manufacture of items of stone, such as mortars, lathe-turned shale bracelets, tesserae, and opus sectile.59 Stratified stone products appear from the first century A.D. but are chiefly found in a substantial dump of industrial waste emplaced some time after A.D. 296-7. There is no evidence of mosaics themselves at Norden.

Some 1,500-2,000 loose chalk tesserae occurred at Norden in a context of late first-century A.D. date, whereas sawn slabs of this rock made their appearance from the second century. The lithology of particular interest is described as 'a brown or black mudstone', suggested without evidence to be of local origin and to have 'possibly come from the [highest Jurassic] Purbeck Beds'; earlier, at Fishbourne, this material had similarly been claimed to be, amongst other things, 'a Jurassic, possibly Kimmeridge, shale'.60 A total of eight loose 'mudstone' tesserae were found at Norden, stratified in layers dating from the second to the fourth century A.D. Unstratified examples were also encountered. Numbers of sawn slabs of 'mudstone' for inlay and other decorative purposes had a stratigraphical distribution from the late first to early second century (1), through the second (13) and late second to late third centuries (7), to the late third to fourth century (8). A findspot c. 100 m to the south-west of the excavation yielded 20 'small grey cubes', presumably tesserae, of what had been described as 'a slightly calcareous siltstone'.61 This may also be the 'mudstone' of the main site. No other lithologies are known as tesserae at Norden.

Stonework described as from Norden and other representative material were examined at the Dorset County Museum, Dorchester.62 The collections include one modular tessera (4.1 g) measuring c. 12 mm along each side, and three double-tesserae (7.2-13.2 g), all on the large side compared to the corresponding forms at Insula IX, Silchester (FIG. 2A). The lithology in hand-specimen is a dark yellowish-grey, weakly effervescent cementstone. A thin-section from a double-tessera revealed a finely granular dolomite rock rich in translucent, brown, amorphous organic matter, scattered opaque organic material, and a little pyrite and quartz silt (FIG. 4F). A very little interstitial calcite was seen. Also present was a small fish bone and a few scales, and a plane-chambered foraminifera. Also with fish scales and a fragment of spinose (?)crustacean shell, a closely similar rock was apparent in thin-sections from two pieces of opus sectile. These preparations were large enough to reveal a coarse lamination or fine banding created by variations in the amounts of amorphous and opaque organic material in the rock. A piece of opus sectile and a lump of unsawn, raw cementstone gave the mineralogical compositions listed in Table 2. These are closely comparable to the cementstone from the Kimmeridge Clay Formation (FIG. 3C, Table 2). An immature Deltoidium, an Upper Jurassic oyster, occurs in mouldic preservation in one sawn piece, and the lump of raw material is also fossiliferous.

This varied evidence leaves little doubt that the tesserae and opus sectile of 'mudstone' found at Norden were procured from dolomite cementstones in the Kimmeridge Clay Formation and not, as has been proposed,63 from the highest Jurassic Purbeck Beds, which the rocks do not resemble. The nearest and most likely source is the outcrop on the coast of the Isle of Purbeck, as near as 6 km to the south-west of Corfe Castle. However, another mudstone, apparently from the local Bagshot Beds (Tertiary), was used for tesserae at the waterside site of Ower, on the shores of Poole Harbour 5.5 km to the north-east of Norden.64 As at Norden there was (rich) evidence of shale-working.

58 Sunter 1986. 59 Thomas 1986. 60 Thomas 1986, 35-6; Cunliffe 1971b, 41. 61 Farrar 1964; Sunter 1986, 11. 62 Peter Woodward kindly facilitated this examination. 63 Thomas 1986, 35-6. 64 Woodward 1986.


DISCUSSION AND CONCLUSIONS

We summarise above a geological analysis of a selection of mosaic materials and decorative stonework at a range of the earliest Roman military and civil/public sites ranged across southern Britain. Because most of the materials involved are fine-grained, the work has necessarily and crucially demanded the application, wherever samples were available, of microscopic and mineralogical techniques. In one important case, critical palaeontological evidence was secured.

The results link tesserae and mosaics across three insulae at Silchester, and lead to the expectation of the even wider use of the same components for decorative floors in the town. On a regional scale, they suggest that the same small range of geological materials - hard white chalk, dolomite cementstone, red burnt mudrock, and yellow burnt mudrock - was employed decoratively almost everywhere, from Kent to Devon to south-east Wales (FIG. 1, Table 3). On the face of it, no geological evidence is hereby offered for the existence of mosaic 'schools' or 'groupings' at the early time we consider, but great caution is necessary on this particular issue. Because of the huge variation in sample size, the absence of a category at a site need not necessarily mean that it was not exploited there. The largest samples come from Insula IX at Silchester and from Fishbourne. Twenty-two categories of material are recognised at the former (Table 1), but these tesserae, being loose, could be analysed petrographically and mineralogically at will. At Fishbourne, apparently with a narrower range of materials, there are hugely more tesserae, but most are in mosaics subject to hand-lens inspection only. At the other extreme, a mere handful of material was available from some sites.

As the evidence currently stands, the suite of widespread materials - dolomite cementstone and the two burnt mudrocks (we have not attempted to provenance the chalk)- was procured from the Kimmeridge Clay Formation of the Dorset coast. This Upper Jurassic unit has two main outcrops, around Kimmeridge Bay in south-west Isle of Purbeck, and from Portesham to Ringstead Bay to the north and east of Weymouth (FIG. 1). A minor but coastal outcrop occurs on the east side of the Isle of Portland.

An important question is where were these materials being processed into tesserae and opus sectile. Corfe Castle is only c. 6 km to the north-east of Kimmeridge Bay and a similar distance from

TABLE 3. DISTRIBUTION OF MOSAIC MATERIALS BY CATEGORY AND SITE.

dolomite yellow red 'local' imported ceramics glass burnt burnt rocks' marble mudrock mudrock

Insula IX, X X X X - X X Silchester

Museum of X - - X - X Reading Mosaic 1

Museum of X ? X Reading Mosaic 2

Exeter X - - X - X Fishbourne Roman X X X X - X

Palace Eccles villa X X X X - X Angmering villa X ? X X X London (all sites) X - ? X Caerleon X X X X - X Norden, Corfe X - - X

Castle

Isandstones, chalk and other limestones, flint


the shores of Poole Harbour, the focus of major late Iron Age-Roman industries that included the production of a range of widely-traded products in stone. The evidence from Norden shows that the cementstone was being shaped there into both opus sectile and tesserae, but of the burnt mudrocks there is no known trace. Moreover, there is so far nothing to indicate that this workshop was intended to serve a nearby building under construction. At the builders' yard at Fishbourne, however, burnt mudrocks as well as the cementstone were being made into geometrical tiles and inlay using imported raw materials, apparently for an adjacent building, with tesserae of these rocks appearing in the slightly later palace mosaics. Lying c. 100 km to the east of the nearest possible sources of these rocks, Fishbourne is not a plausible site for a general manufactory with a similar status to Norden.

Most of the mosaics and materials which are well dated belong to the period between the mid-first century and the early second century A.D. There is a confident pre-Boudiccan attribution of what we now understand to be Kimmeridgian cementstone from London (Southwark), and it is not unlikely that the material from the legionary bath-house at Exeter pre-dates A.D. 60. The rock from the builders' working yard of the 'proto-palace' at Fishbourne, which includes coloured as well as black and white material, is of Neronian-early Flavian date,65 while the best-dated floors are to be found at Fishbourne and Caerleon from c. A.D. 75. None of our examples has a terminus post quem which is definitely after A.D. 100, but several are assigned a 'late first/early second century' date range. The secondary, Period III floor in Room N7 as excavated at Fishbourne, the celebrated 'Dolphin' mosaic, makes significant use of ceramic and limestone tesserae to produce colours ranging, in the case of the former, from bright red to reddish black, and yellow-orange in the case of the latter. This floor dates after c. A.D. 160 and the Kimmeridgian material is no longer dominant. This is also the case of the Period III floor in N13. Is this because Dorset rocks were no longer being exploited with the same intensity as before and were simply being recycled into new floors? Do the Period III floors provide a terminus ante quem for the intensive exploitation of those materials?

This chronological range compares well with that of the main period of production of Purbeck marble for both monumental inscriptions and decorative purposes, as used internally for opus sectile mouldings, wall inlay and furniture inlay, and as used classically at Caerleon, Exeter, Fishbourne, London, and Silchester. Just as our latest mosaic floors with dominant Kimmeridgian materials have first century A.D. termini post quos, so, with the exception of at least one tombstone, none of the independently dated fragments of Purbeck marble used for monumental inscriptions is later than the end of the first century A.D.66

Nevertheless, determining an end-date for the significant exploitation of both Purbeck marble and our Kimmeridgian rocks for building purposes is not straightforward. Mosaics aside, most of the tesserae we describe occur out of their original context, and it is usually difficult to distinguish between a piece which has been discarded fresh from working into a primary context associated with construction and one which has been recycled for a new floor or discarded as rubbish following demolition of a building. Sometimes the survival of signs of wear or of adhering mortar may give a clue as to whether a tessera has been used, but surfaces can become softened and rounded, and calcareous matter dissolved, as the result of weathering at a site. This issue is brought sharply into focus by ornamental stonework in London.67 Of 56 examples of Purbeck marble from first- and third-century A.D. contexts, more than half (31) are from those dated '2nd+, 3rd and 3rd+', and only one of these was found in situ in a second-century A.D. bath-house.68 A similar picture is presented for early finds of 'Wealden shale' opus sectile (Kimmeridgian cementstone), where six of the eight

65 Although Cunliffe (1971a, 63) only notes a black and white mosaic fragment and white tesserae from this Period IC First Masonry Building.

66 Dunning 1949; Frere and Fulford 2002, 173; for a general summary of the use of Purbeck marble in Roman Britain, see Williams 2002.

67 Pritchard 1986. 68 Pritchard 1986, 169-71.


examples stratified over the same time range are from third-century A.D. and later contexts.69 It is clearly improbable to suppose rising production of Purbeck marble and Kimmeridgian material long after the main phase of building which required these materials had ceased by about the mid-second century A.D.70 We return to the issue of the end-date of production below.

In recognising the close proximity of the sources of Purbeck marble and the Kimmeridgian materials, we should not overlook the question of the provenance of the chalk tesserae. Our prior hypothesis, however, is that, in large measure at least, and in the early period of mosaic manufacture, they, too, were procured from the coast, as has been suggested for Exeter, Fishbourne, and Norden, but proof must await extensive micropalaeontological work beyond the scope of this paper.

Altogether, the Kimmeridgian rocks of Dorset, probably in their coastal outcrops, provided the essential, if minimal, range of materials with their associated colours for the interior decor of military, public, and private buildings.71 These could be - and were - supplemented in small quantities at individual sites by other lithologies, some comparatively local but others, marbles in particular, possibly from overseas (Table 3). As we note above, at Silchester (Insula IX), Fishbourne, London (Winchester Palace), Eccles, and Caerleon, rock plausibly from nearby sources (e.g. Lias at Caerleon) was being used alongside the predominant, far-travelled materials from Dorset. At Angmering, however, the supplements may have come partly or wholly from overseas.

Our conclusion that there was a 'package' of quality building materials available from a restricted geographical area raises questions about the organisation of production and distribution. Present evidence suggests that there was a workshop at Corfe Castle producing cementstone opus sectile and tesserae for general distribution, but that raw cementstone and burnt mudrock were brought a considerable distance to be worked up at one building site, that of the 'proto-palace' at Fishbourne. The workshop at Norden arguably drew raw material from the nearby Kimmeridge Bay outcrop (FIG. 1). Fishbourne need not have been supplied from there but could have drawn upon the Kimmeridge Clay Formation at Ringstead Bay to the west, although the upper part of the Formation is less well-exposed here. That tesserae of burnt mudrocks are widespread, and that opus sectile in these materials is not confined to Fishbourne, suggests that there was somewhere at least one workshop that exploited, or even restricted itself to, the mudrocks. Hence a model of dispersed production including both the initial quarrying and the subsequent shaping of the stone seems at present apposite. How far shaping of the tesserae was driven by fashion as opposed to workshop tradition requires much further investigation, but we can detect slight differences in modularity between Eccles, Fishbourne, and Silchester which might hint at different workshops or artists.

There are clearly significant organisational implications in co-ordinating the quarrying and working of the range of geological materials which were being deployed in a number of building programmes across southern Britain, from legionary fortresses to high-status villas, town-houses and other, quite modest urban buildings such as the timber-framed structures in London west of the Walbrook or in Southwark. These materials were thus available at all levels of society - military, public, and private - that were capable of exploiting or affording them. While there might have been an issue about the availability of the coloured stones of reds and yellows (we note, for example, the use of samian for red at Exeter), it is difficult to know whether this was driven in part at least by a preference for bichrome floors.

The mixed pattern of working the material to the desired shape both near the geological origin, as at Norden, and at the point of consumption, as at Fishbourne, is reminiscent of the pattern of working of Kimmeridge shale from the Iron Age and through the Roman period. Several settlement sites on

69 Pritchard 1986, 186. 70 For London, see Perring 1991; a more general survey of towns appears in Wacher 1995. 71 For Romano-British settlements associated with the working of Purbeck marble in south-east Dorset, see RCHME

1970, 602-13.


the Isle of Purbeck yielded waste from the lathe-turning of shale to produce armlets72 and similar waste is also found at sites, such as Silchester, remote from the geological origin.73 While this might be seen as evidence of a continuity of tradition of working from Iron Age into Roman, it has to be remembered that the shale was used not for building but for other purposes, including ornamentation of the body. The exploitation of Kimmeridgian cementstones and burnt mudrocks, Purbeck marble and chalk for interior decor, including walls and floors, appears to have been a purely 'Roman' innovation after A.D. 43.

The sheer volume of material demanded for major projects, like the fitting out of a bath-house as at Exeter or Caerleon, or of major villas like the Neronian-Flavian buildings at Fishbourne, suggests a different kind and level of organisation. For example, given the modular size (Silchester), and allowing for mortar, a single mosaic floor of 25 m2 requires c. 200,000 tesserae amounting to half a metric tonne of prepared rock. The consequential waste could well have been several times that amount. It is striking that the industry was capable of supplying these quantities of material to such a wide variety of destinations at more or less the same (archaeological) time and with little need to look elsewhere for additional resources. Distance does not seem to have affected availability (and cost) across the breadth of southern Britain. The organisational leap from simply supplying shale for mostly personal and ornamental purposes to the deployment of building materials represents a step- change. Like metals such as lead and iron, such resources were part of the emperor's domain and, in the case of the south-east Dorset exploitation, were presumably mediated through the procurator and/or Legion II. Whether these materials were made available at 'market' prices can only be guessed at, but both their distribution in modest as well as grand establishments, and their competitive success suggest some form of subsidy. In the case of mosaics in particular, a number of options, including the use of both ceramics and glass, represented a realistic, accessible and, partly at least, satisfactory alternative. Provision of decorative building materials at subsidised prices may have been a deliberate way of assisting the native aristocracies to become 'Roman'. Alternatively, attractive loans may have made the acquisition of these materials irresistible. Although the process of exploitation begins before Boudicca, it continues in the Flavian period and into the second century A.D. In the latter contexts, this represents the kind of encouragement that Tacitus credits Agricola with in his exhortation to the natives to build templa, fora, domos.74 In the former, however, and in contrast, the acquisition of decorative stone may have been one of the factors which pushed the aristocracy into too much debt and encouraged the calling-in of loans in the late 50s prior to the Boudiccan revolt.75

One further reason for reflecting on the agency responsible for the exploitation and supply is that, if an official activity, its duration and intensity may bear no relation to the scale of demand for the materials. Although determining the end-date for supply is hard, not least because of the possibility of re-use in later mosaics, it is worth recalling the major change that took place in south-east Dorset activity in the early second century A.D. The archaeological record reveals a very significant expansion in the production and distribution of black-burnished type pottery (SEDBB 1) from around the shores of Poole Harbour from the reign of Hadrian in the 120s and onwards.76 The scale of this production is not insignificant and it could be connected with the exploitation of salt. It is tempting, therefore, to see a connection between the decline in the exploitation of Kimmeridgian rocks, Purbeck marble, and chalk from south-east Dorset and the expansion of the pottery industry and, possibly, salt extraction. Such a substitution could be effected by making use of and redeploying elements of the local population from stone exploitation to pottery- and salt-making, and by redirecting the transport system. For both to have operated concurrently through the second and into the third centuries A.D.

72 RCHME 1970, 499, 510, 597-602, 604, 608-9, 620-1; Sunter 1986; Woodward 1986. 73 Lawson 1975, 256. 74 Agricola 21. 75 Dio Cassius 62.2. 76 Allen and Fulford 1996.


has significant implications for settlement and population in south-east Dorset and elsewhere in Britain.77

Finally, we return to the tesserae and the floors made from them. Apart from some near-pristine Period II mosaics at Fishbourne, little more than fragments of floors survive from elsewhere, but, with one well preserved border in black and white, it is appropriate at least to add the Insula XIX mosaic from Silchester to the number of early mosaics from Britain; the latter should also include the well- preserved bichrome floor from House 1 in Insula XIV. In this situation where little has survived it is difficult, as we note, to define schools, let alone groupings of style or workshops, though an expectation of several firms operating across southern Britain in the later first and early second century A.D. is attractive. The indicative scale of consumption at London and Silchester alone would argue for the probability of multiple workshops or groups of itinerant craftsmen. The occurrence of particular traits, such as the size and shaping of the tesserae and the selection of certain materials, for example, the consistent choice of samian for red at legionary Exeter, may provide pointers toward the identification of workshops. On the other hand, the evidence from Exeter, Eccles, Angmering, and Caerleon hints in the case of bath-houses at a utilitarian preference for double-tesserae set on end, perhaps as a protection against seeping damp. The image, admittedly heavily weighted by the Period II examples at Fishbourne, is of a preponderance of bichrome floors in the earliest phase of mosaic-making in Britain. However, the presence of coloured material in abundance at the Neronian-early Flavian builders' yard, and its incidence at Silchester from later first- and second-century A.D. contexts and floors, suggests that the ratio of polychrome to bichrome was greater than is implied by those early fragments which have survived. Equally, even if we cannot be confident of an association with an actual pavement in the pre-Boudiccan period, the presence of the materials themselves is strong, indirect confirmation of the presence of pre-Flavian mosaics in fortress, town and country in early Roman Britain.

PALAEONTOLOGICAL NOTE

By J.A. Todd and N.J. Morris78

The fossiliferous material we have examined comprises three centimetre-scale fragments from Insula IX, Silchester, and a decimetre-scale lump of raw material excavated at Fishbourne, probably from the builders' yard associated with the Neronian-Flavian 'proto-palace'. Although with marine fossils, notably oyster spat and fish bones (especially skull bones) of broadly Mesozoic-Tertiary age, the two cementstone tesserae (lithology La) from Insula IX yielded nothing of any precise stratigraphical significance, and are not considered further.

The piece of burnt red mudrock from Insula IX (lithology Mc) gave several fossils in largely mouldic preservation with occasional baked adherent shell carbonate. We found two compressed specimens of small heterodont bivalve mollusc, but without details of the hinge or ligament; one external mould of a pteriomorph bivalve, probably an ostreoid oyster; two fragments of gastropod shell with striate and nodose sculpture; and one rugose shell fragment, probably from a bivalve mollusc. The small bivalves are similar in shape to forms that occur particularly from the Jurassic onwards. The ostreoid (true) oysters and high-spired gastropods with ornamentation similar to that observed (superfamily Cerithioidea) are compatible with the age-range suggested by the heterodont bivalves.

Of greater stratigraphical value is the large, fragmentary lump of burnt red mudrock (lithology Mc) from Fishbourne. This preserves the external mould of an incomplete large ammonite and c. 10 isolated valves, whole and fragmentary, of bivalves present as internal or external moulds with baked shell present. Also present in mouldic preservation are at least two moderately high-spired gastropod

77 cf. Allen and Fulford 1996, 251-61; note also the logistics associated with the contemporary construction of Hadrian's Wall in Kendal 1996.

78 Both authors are of The Natural History Museum, London.


shells. The amount of detail preserved on the ammonite allows it to be confidently attributed to the genus Pectinatites Buckman, of the family Perisphinctidae. The gastropods belong to a species characterised by its sharply carinate spire whorls and a final whorl that is bicarinate with a long, thin and curved anterior canal. These features allow a confident identification as Dicroloma Gabb, an apporhaid gastropod ranging from Early to Late Jurassic, and in Britain commonly found in the Oxford Clay and Kimmeridge Clay Formations.79 The ovate bivalves are poorly preserved and are difficult to identify with confidence, but a few specimens show on the hinge a bifid cardinal tooth and traces of long anterior and posterior lateral teeth, confirming that they are heterodonts. With their smooth ventral margin, small size (length 5 mm), and very fine concentrically-ribbed ornament, these bivalves probably belong to the genus Isocyprina (Venericyprina) of the family Arcticidae. About five species are known from the English Kimmeridgian Stage,so and the Fishbourne material is comparable with I. (V.) miniscula Blake of the Upper Kimmeridgian of South-West England.

Only the Fishbourne sample provides a tightly-constrained age and our conclusions are based largely on this material. The occurrence of the narrow-ranging ammonite Pectinatites shows lithology Mc at the Fishbourne Palace builders' yard to be of Lower Volgian age in the Upper Jurassic, and fully supports the proposal, reached on other grounds explained in the main text, that this burnt mudrock comes from the (upper) Kimmeridge Clay Formation. In South-West England, as typified by the Kimmeridge Bay outcrop (FIG. 1 above), the gastropod Dicroloma and the bivalve Isocyprina (Venericyprina) are both common in and characteristic of the upper Kimmeridge Clay Formation. The Silchester fragment is likely to have the same provenance, for the heterodont bivalves may represent Isocyprina and the cerithioid gastropod fragments have a morphology entirely consistent with those members of the Procerithiidae which can occur abundantly in the Kimmeridge Clay Formation. It is interesting to note that, under today's conditions, the upper Kimmeridge Clay Formation is best exposed on the coast to the east of Kimmeridge Bay in the Isle of Purbeck.

ACKNOWLEDGEMENTS

We gratefully acknowledge the help and interest of many people who generously allowed us access to sites and material in their charge: John Allan (Royal Albert Museum & Art Gallery, Exeter), Richard Brewer (National Museum & Gallery, Cardiff), Rebecca Fardell (Littlehampton Museum), Jill Greenaway (Museum of Reading), Jennifer Hall (Museum of London), Mark Lewis (Roman Legionary Museum, Caerleon), Susan Pringle (Museum of London), David Neal (Milton Keynes), David Rudkin (Fishbourne Roman Palace, Chichester), John Shepherd (Museum of London), and Peter Woodward (Dorset County Museum, Dorchester). Ian West (University of Southampton) kindly provided information on sites of burning in Jurassic shales of the Dorset coast. We are grateful to Kevin Hayward for help, and to Bruce Sellwood for valuable comments on some of the rare lithologies at Silchester. We are indebted to our colleagues Michael Andrews and John Jack for respectively mineralogical analyses and thin-sections prepared with great skill from mostly very small samples. Especial thanks go to Jon Todd and Noel Morris (The Natural History Museum, London) for their rich palaeontological findings from our very limited material.

Department ofArchaeology, School of Human and Environmental Sciences, University of Reading [email protected] [email protected]

This paper is published with the aid of a grant from the University of Reading

79 Wignall 1990, 9, 11-12; Hollingworth 1991, 80-1. 80 Clausen and Wignall 1988, 131-6.


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Documents

Early Roman Mosaic Materials in Southern Britain, J.R.L, Allen, M.G, Fulford