96 NATURE | VOL 427 | 8 JANUARY 2004 | www.nature.com/nature

Automatic archaeologyDigging in the dirt in search of clues to the past has churned up millions ofpieces of pottery. Haim Watzman unearths the new technologies beingdeveloped to sift through them all.

Vered Rosen is an artist. For the pastfew years, she has made her livingdrawing pieces of pottery using a

simple sketchpad and a pencil, for a team ofarchaeologists excavating Tel Dor on thenorthern Mediterranean coast of Israel,south of Haifa. But now her employers areretraining her. They have sent her to theWeizmann Institute of Science in Rehovotto learn to draw using a profilograph, adevice that can produce digital images ofpottery fragments — images that can beanalysed and classified by a computer.

For archaeologists, the ability to sift auto-matically through pottery samples is fastbecoming a necessity. A typical excavationsite might disgorge hundreds of thousandsof pieces of broken clay pots — the favouredall-purpose vessels from ancient times untilwell into the Middle Ages — all of whichneed to be washed, sorted, labelled andanalysed. The pots’ shapes, dimensions, tex-ture and style can help to date the layers ofsoil through which the archaeologists aredigging,and can even reveal when and wheredifferent societies were trading with eachother.Pottery shards are, to an archaeologist,as important as microfossils are to a palaeo-climatologist — the crucial clues that areused both to date a stratum and to under-stand the conditions that prevailed at thetime. But there are not enough trained peo-ple to deal with the flood of pottery finds,andthere are doubts in the community aboutwhether the conventional method of hand-drawing is the best way to study them.

Artistic differenceRosen’s metamorphosis from artist to tech-nician began when Uzy Smilansky — aphysicist at the Weizmann Institute and anarchaeological hobbyist — celebrated hissixtieth birthday three years ago. On thatday he took his entire family to an excava-tion at Ein Gedi, on the northwest coast ofthe Dead Sea. “At the time I was looking forsomething new to do in the last phase of mycareer,” says Smilansky. His experience as anamateur archaeologist meant that he wasaware of the problem of comparing andanalysing vast quantities of pottery. And hisexcavation holiday drove that home. “Ithought it was time to harness the computerto the profession of archaeology,” he says.

With that goal in mind, Smilansky wasdirected to Ilan Sharon of the Hebrew Uni-versity of Jerusalem. Sharon, one of the chief

excavators at Tel Dor, has a similarly mixedbackground, having done two years ofundergraduate work in mathematics beforeswitching to archaeology.Sharon was enthu-siastic about Smilansky’s idea, and knew of aHebrew University undergraduate namedAvshalom Karasik who was doing a doublemajor in archaeology and mathematics.Together with Ayelet Gilboa of the Universityof Haifa — the Tel Dor excavation’s potteryexpert — they made a perfect team.

Together, they soon learned that othershave been in hot pursuit of new ways tostudy pottery in bulk. Statistician CliveOrton of University College London wasone of the first to outline the potential bene-fits of speed and objectivity that an auto-mated system could offer1. In the late 1980s,Orton began to work on one of the first com-puter programs that can analyse and com-pare information about large quantities of

shards. But measurements for each piecehad to be painstakingly taken and enteredinto the computer by hand.

Drawing on technologySmilansky’s team focused its efforts on elimi-nating that problem with the help of a pro-filograph. The device, invented years ago foruse by architects, designers, artists and scien-tists, resembles a cross between a draftingtable, a caliper and a computer mouse. Touse it, a piece of pottery is clamped above thetable in a position such that the central axisof the pot, if it were whole, would run paral-lel to the table. Then a delicate metal pointerattached to a computer mouse is used totrace the outline of the pot, clicking everyfew millimetres. This forms a series of datapoints in three-dimensional space that thecomputer then connects to create an imageof the shard’s surface.

Rosen is still learning how to use thedevice. At this point, she says, it takes herabout an hour to trace a single piece — muchlonger than the 20 minutes it would take todo a simple pencil drawing of the fragment.But the end result is much more accurate andobjective than any freehand drawing.

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Helping hand: Uzy Smilansky (left) aims to use adrawing device called a profilograph to recordthe wealth of pottery shards (right) unearthed atsites such as Tel Dor (above and above right).

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Smilansky’s role, meanwhile, has been toprogram the computer to interpret thesedrawings. His program creates a ‘curvaturefunction’ from the lines — a mathematicalrepresentation of features such as the shapeand size of the pot. For the moment, his pro-gram emphasizes the shape of the top fewcentimetres and rim of the pot — a diagnos-tic characteristic that many archaeologiststhink is the best indicator of when and bywhom the pot was made.

The technique’s great advantage is itsobjectivity. “Hand drawings are inevitablybiased, no matter how objective they try tobe,” says Gilboa. “The artist will often havethe excavator’s theories in mind when look-ing at a piece, and when the archaeologistreviews the drawing he’ll often tell the artistto emphasize a feature that he thinks isimportant.”

“Most drawings are not accurate,” agrees

Robert Sablatnig, a computer scientist at theVienna University of Technology in Austria.“Archaeologists somehow classify their find-ings in their mind and then draw what theythink they should draw to make the classifi-cation correct. When you examine the origi-nal fragments, they often don’t have the samefeatures as in the drawing.”

To test the usefulness of the profilograph,Gilboa, Karasik, Sharon and Smilanskyturned their attention to an ongoing disputeabout evidence of trade between Hazor, a sitenorth of the Sea of Galilee that was a majorurban centre during the Iron Age, and Tyre, acity in modern-day Lebanon that was once amajor Phoenician port. A large bulk of evi-dence points to the fact that these two nearbycities were engaged in trade. But there havebeen arguments about whether there is addi-tional evidence for this in the large collectionsof ‘torpedo’ jars found at both sites. These

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long, cylindrical vessels, used in the northernKingdom of Israel and Phoenecia during theIron Age IIB period, about 2,800 years ago,were made to carry anything from grain towine in commercial trade.

One of the Hazor researchers argues thatall of these jars were manufactured in Hazor,and that some were exported to Tyre2.But thearchaeologist who found the jars in Tyreclaims that, if anything, they went in theopposite direction — the Hazor jars wereimported from Tyre3. A third study, byGilboa, argued that the existence of tiny, butconsistent, morphological differencesbetween the Tyre and Hazor jars indicatesthat the jars are not the same at all, but wereeach made in their own home city4. Testsusing the profilograph backed up Gilboa’scontention — the jars from each city are farmore similar to each other than to those fromthe neighbouring area. The discovery mightnot help to clear up any confusion abouttrade between the two cities, but it does showthat archaeologists can benefit from a stan-dard, objective system to judge similaritiesand differences in pottery.

Subjective viewBut even Smilansky’s technique cannotremove all subjectivity from the process —someone had to decree that rim shape isamong the best deterministic factors, forexample. “We began with a great deal ofrespect for archaeologists,” Sharon says.“Our assumption is that the computer’s job is to provide an emulation of thearchaeologist’s intuitive processes — with a grain of salt.”

Nor will something as simple as an equa-tion describing the rim of a pot ever completelyreplace the watchful eye of a trained archaeol-ogist. “There’s a lot more to identifying pottery than looking at drawings,” says JodiMagness of the University of North Carolinaat Chapel Hill, an expert on Roman pottery.“It also involves familiarity with the fabric,which means things like colour and texture.You have to handle a lot of pottery to becomefamiliar with it. Some pottery experts eventaste pot shards to identify them.”

“There’s something about the humanmind’s ability to deal with data that so farcomputers don’t do,” says Aren Maier ofIsrael’s Bar-Ilan University, who excavates atTell es-Safi, a site southwest of Jerusalem.Maier is so far sceptical of the value of thesimple drawings produced by computer pro-grams such as Smilansky’s. But, he adds, “itcould be that that’s enough — especiallygiven our need to save time, space andresources”.

That is exactly what the profilographtechnique promises to do. “What do you dowhen you have 100,000 pot shards?” asksGilboa. There are simply not enough artiststo cover that much work. “There’s no ques-tion that there’s a ton of pottery and not

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enough people who can work on it,” saysMaier. Part of the problem is that drawingand comparing bits of pottery is seen as anunglamorous job. “It’s the kind of work yougenerally do for a doctorate and then nevertouch again,” says Gilboa. “The general feel-ing in the field — it’s totally mistaken, ofcourse — is that the study of pottery is forwusses,”adds Maier.

But that means that masses of potteryfrom a site such as Tel Dor are never drawn oranalysed,potentially leaving interesting factsundiscovered.

One reason that Tel Dor was chosen as alaboratory for automatic analysis is that thepottery in the area changed relatively rapidlyover time, with fashions in the city shiftingevery few decades. During Israel’s iron age,around 3,200–2,600 years ago, the profiles ofpots shifted from looking like bent femurbones — with knobs and indentationsadorning the top — to simpler S-shaped pro-files resembling the horn of a longhorn cow,passing through myriad styles in between.

An archaeologist who chooses to publishdrawings and studies of only one or even ahandful of these pieces will probably misssomething that could provide excavators atanother site with crucial information aboutrelations between the two communities,says Gilboa. Even if all the pottery is drawnand analysed by hand, it is likely that few people will bother to look them up in theweighty excavation reports — a process soslow and laborious that it is seldom carriedout, she adds.

An automatic technique, together with acomputerized database of the results, wouldsolve these problems. But the profilograph isnot the only possible technological solution.Sablatnig, for example, is working on a different experimental system that uses photographs to form a three-dimensional

computer image of a broken pot. Thisprocess is faster than using a profilograph, soSablatnig does not restrict himself to lookingat the tops of pots.As a result,he gains a morecomplete picture of the reconstructed piece.But so far it is unclear which method willprove more powerful in comparative studies.Smilansky points out that his own curvaturefunctions are more versatile than Sablatnig’s,as archaeologists can use them to specify theaspect of a pot’s shape in which they are mostinterested. The pair plan to collaborate todevise the best possible method — oneoption that Smilansky is already investigat-ing is the possibility of using lasers to imagethe pieces.

Shaping upOthers, including research teams at BrownUniversity in Providence, Rhode Island, andArizona State University in Tempe, are alsotackling the problem.

But many of these systems suffer from thefact that they address only one element of thepottery — its shape. What’s more, to recon-struct the image of a pot from a few shards,they assume that the vessels they are lookingat are basically symmetrical. Prudence Rice,an archaeologist at Southern Illinois Univer-sity in Carbondale, points out that peoplefrom the Americas did not use potter’swheels, so this assumption does not apply topieces from the New World.

Instead, archaeologists rely more heavilyon other criteria, such as colour or the com-position of the clay, to identify such pieces.“Idon’t see how these three-dimensionalimages are going to replace that,” says Rice.Smilansky and Sablatnig are working togetherto develop imaging methods that can cap-ture features such as painted pictures on thepots.And Orton,one of the pioneers of auto-mated comparative archaeology, is working

on adding information about colour, textureand clay type into his databases of potteryshards. But he has not been able to automatethe collection of that kind of data — he is stilldoing it all by hand.

In the end, even if these teams succeed inestablishing profilographs or laser-imagersas standard equipment on archaeologicaldigs, the kind of comparisons that Gilboawants to carry out will also require back-logging information from previously pub-lished excavations into a computer format— an immense amount of work that Rosenand her colleagues could never achieve.Gilboa nevertheless dreams of an interna-tional and comprehensive pottery databasethat will make serious comparative work notonly possible,but a pleasure.Maybe then,shethinks, archaeologists can begin to answerquestions that they have not yet been able toaddress, such as whether pot shape changedover time because of fashion trends, newtechnologies or both. Who knows? Maybeworking on pottery will even become glamorous again. ■

Haim Watzman is a freelance writer in Jerusalem.1. Orton, C. Sampling in Archaeology (Cambridge Univ. Press,

Cambridge, 2000).

2. Geva, S. Bull. Am. Sch. Oriental Res. 248, 69–72 (1984).

3. Bikai, P. M. Bull. Am. Sch. Oriental Res. 258, 71–72 (1985).

4. Gilboa, A. Qedem Rep. 2, 15 (1995).

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Given the wealth of findings from Tel Dor (above and right), a computer log of pottery shape will be a huge bonus. Future databases will also aim to incorporate information on clay type and colour.

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