Surveying Instruments of Greece and Rome (review)

Surveying Instruments of Greece and Rome. By M. J. T. Lewis. Cambridge: Cambridge University Press, 2001. Pp. xx+389. $80.

This is a most welcome addition to the collection of textbooks on Greek and Roman technology that have appeared over the past two decades. Civil engineering was an important element in Greek and Roman culture, and M. J. T. Lewis offers the most detailed interpretation of instruments and techniques to date. The ancient written treatises are the principal source, and here Lewis is able to add to the well-known Greek and Latin writers some later texts in Arabic, Hebrew, and Syriac. The material evidence for the instruments is unfortunately very sparse, and in one case (the libra) entirely lacking, but what survives is carefully analyzed. Perhaps Lewis's most original and interesting contribution comes from his account of his own reconstruction and testing of ancient instruments, which was no doubt helped by his practical experience of archaeological surveying.

The book is divided into three parts. In the first, Lewis explains, very clearly and concisely, the various activities of the surveyor: measuring distances, orientation and setting of right angles, measuring heights, leveling and road alignment. He then discusses the most commonly mentioned instrument, the dioptra, making the important point that its name means "something to look through," that is, a sighting tube. Lewis considers that the simplest form of the instrument could be used very effectively for horizontal or vertical sighting, and that the instrument described by Hero of Alexandria was a specialist (and very expensive) version that was not in general use.

The next instrument is the libra, clearly a very important device for Roman surveyors (libratores) for which we have virtually no written or material evidence apart from the name itself (which means the beam of a balance) and the very remarkable feats of aqueduct surveying that, Lewis believes, could hardly have been achieved by any other means. He interprets it as a balanced metal beam hanging from a knife-edge mount, a device he has constructed and tested with very impressive results. At the end of this section he deals with the groma used for setting out rectangular plots and the hodometer for measuring long distances.

The second part of the book deals in great detail with the practical applications of these devices. Lewis begins with a semiastronomical problem: the measurements of the earth made by Eratosthenes and others, and the possible sources of error. He goes on to the measurement of mountain heights and the activities so vital for the development of the Roman empire: surveying for canals and aqueducts, tunnels and roads. Lewis's extensive knowledge of archaeological sites all over the Greek and Roman worlds makes his account very full and comprehensive.

In the third part, Lewis considers the source texts and their interpretation. Hero of Alexandria's Dioptra is reproduced in full, with detailed commentary. This includes a description of the instrument itself, and a number of procedures for its use, plus the hodometer, and a garbled description of a naval version—a primitive ship's log. There are also excerpts from many other authors, ranging in date from the twelfth century B.C.E. to the first.

In a review of this brevity, one can only speak in very general terms. Lewis's writing is clear and direct, and his explanations easily understandable. He is, however, dealing in minute detail with some difficult and vexed questions, and he has in mind a reader with a strong interest in the subject and a very inquiring mind (and an accessible reference library, hence the very full bibliography). The book is an interesting and informative read, but not always an easy one. If I have one criticism to offer, it is that a number of contexts could have been made clearer by means of more diagrams and fewer words (for example, the hodometer on pp. 283-85). When all is said and done, however, this...