For anyone interested in ancient technology, classical architecture or the history of science, this is a very important book. For anyone serious about retracing monument siting methods, hypothetically reconstructing ancient landscapes or understanding the planning of settlements in Antiquity, this book is indispensable. The work of M. J. T. Lewis (MJTL) is thoroughly researched, well referenced and brings to light a host of sources previously neglected. Not since publications like Jean-Pierre Adam's La construction romaine (Picard, 1989) have we been provided with such a sound means with which to assess specific surveying instruments: MJTL presents reconstructed devices that test and challenge existing descriptions and archaeological interpretations; the two reconstructed instruments that he presents and assesses, the dioptra and libra, have probably never been reconstructed within a comprehensive undertaking like this one.
The book is divided into three broad sections, each corresponding to the author's main research areas. The first section looks at surveying instruments and perhaps more importantly, their methods of use; the second section investigates practical applications of the same devices; and the third section, which is significant in terms of presenting new material that advances current scholarly research, presents related literary sources, many of which have not previously been translated into English, including Arabic, Hebrew, Greek, Latin, and Syriac texts.
After providing initial explanatory notes on cross-referencing specifics, translation difficulties, terminology variations, and gradients and measures, MJTL addresses the fundamentals of surveying (geometry and levelling) in Chapter 1. He then uses Chapter 2 to prepare the reader for the dioptra, the instrument so brilliantly devised by the Greeks to measure heights, levels and angles in both horizontal and vertical planes. Chapter 3 then offers a thorough discussion of the same instrument, all-the-while including a comparanda of the literary sources. Perhaps the most significant aspect of the discussion on the dioptra, however, is the section dealing with a reconstructed, working model. The whole is provided with drawings and photographs that clearly show the operation of the device. In Chapter 4, MJTL does the same for the libra, the instrument used by the Romans to level in the vertical plane (mostly in the construction of aqueducts). In this case, the discussion is rather short, probably because there are so few sources to derive any conclusions from. As with the dioptra, MJTL tests the device's application using a working model in the field; while the model, as the author points out, is speculative and based on fairly sparse evidence, it does render an entirely plausible representation.
The next instrument that MJTL focuses on is the groma in Chapter 5. The tool, probably developed by the Greeks (yet mostly used by Romans), was used to set out straight lines and right angles. The ancient sources are discussed, as well as the models developed by authors during the past decades. As in all of his chapters, MJTL includes the ideas of recent scholars and here he considers the hypothetical renderings of others and assesses them in detail; drawings generated over the last century are provided to render a better portrait of the diverging interpretations. In Chapter 6, the focus is on the hodometer, an instrument used to measure distance travelled. As with the groma, the author considers the sources, albeit briefly. The set of chapters on the instruments ends with the hodometer. A brief summary or synopsis of this first part of the book or a concluding section might have been useful.
The second main section, on the practical applications of the same instruments, begins with a look at the varying results the ancients arrived at in measuring the circumference of the earth (Chapter 7). Here MJTL does not actually reveal "how" instruments would have been used to complement theories and calculations; he does, however, explore the logic behind the calculations used to arrive at specific distances. A table comparing the sources, converting their figures according to the most used values for the stade, is provided at the end of the chapter. The chapter complements the earlier Greek and Roman Maps of O. A. W. Dilke (Johns Hopkins University Press, 1985) and anyone referencing Dilke will find MJTL's chapter particularly helpful in terms of added detail. Mountain height calculations and estimates form the basis for Chapter 8, with Olympus serving as an example. As usual, the various sources (and the authorities cited by the same sources), are compared and assessed, with a summary chart included within the discussion. What is interesting in the conclusion to the chapter is that MJTL finds that the dioptra would have been reliable in less-than-hospitable terrain. The latter most certainly changes the way the instrument has been perceived in terms of its use and dependability.
In Chapter 9, the surveying of canals and aqueducts is broached. While the Nile-Red Sea canal and the Isthmus of Corinth canal are the obvious choices of study (for canals), the aqueduct section is slightly broader, given that they were more prevalent, in terms of large-scale civil engineering works. As with the other chapters in the book, the focus is as much as possible on the sources and this is where MJTL is strongest. Two separate sections are devoted respectively to the impressive, yet to be fully documented, Nîmes aqueduct, and to "the challenges of surveying". Related to these challenges, especially as they involve such difficulties as slope gradients and alignment, are tunnels, the subject of Chapter 10. The discussion is focussed on the four main preoccupations confronting tunnel surveyors: tunnel categories, alignment, levelling, and meeting; helpful are the specific example provided throughout. To the author, tunnels are the most difficult of engineering activities (with the exception of surveying, of course). He is probably correct in this assessment as tunnel construction involves particular challenges in maintaining linear positioning; the discussion renders a clearer portrait of the efforts required for such undertakings in antiquity.
Related to linear positioning, Chapter 11 focuses on Roman roads. This is arguably the most comprehensive section of the "applications section". Specific diagrams illustrate the main points and the researcher involved in Roman urban planning will find the section on "Geometrical Construction" particularly useful. The next chapter (Chapter 12 - Epilogue) addresses some important questions related to the origins of the instruments and their use. MJTL uses Needham's Science and Civilization in China, III: Mathematics and the Sciences of the Heavens and the Earth (Cambridge, 1959) as a main reference to highlight that there were many parallels to the Greek and Roman experiments in surveying in China. Other sources are pulled into the convincing narrative. As with the first section of the book however, this second one does not have a synthesis or conclusion.
In the third part of the book, MJTL takes a very close look at texts that focus closely on survey instruments, as well as other treatises such as Vitruvius' De Architectura Libri Decem, that describe related instruments within their passages. Sections of the writings of Hero of Alexandria (Dioptra), Julius Africanus (Cesti) and Al-Karaji (The Search for Hidden Waters), as well as the Anonymous Byzantinus (Geodesy) are specifically focussed upon. The whole is provided in plain and accessible language which makes it useful for the non-specialist. Some diagrams are used to complement the translated passages. While MJTL does introduce, briefly, the ancient authors, it might have been useful to insert brief biographical summaries (when this is possible) in order to better contextualize the narratives for the reader. Also, it might have been helpful to be more explicit as to what manuscript is being translated; some of these treatises and texts exist in a variety of transcriptions. That said, the importance of these translated passages should not be underestimated; this is certainly the first compendium where so many related sources can be referenced.
In the end, what we are provided with is probably the most useful book on ancient surveying instruments and techniques that has come to light. It is possible that some readers would prefer more examples of survey calculations so that the book might be more readily applicable to specific research problems, but this is not the author's purpose. It is also possible that other readers might look for a more in-depth discussion of surveyors, like the agrimensor, but this too is not the author's intent. The only criticism in terms of comprehensiveness, and MJTL does recognize this, is that a finer look at the groma would have made the work that much more complete; the only criticism in terms of readability is that section summaries might have helped the reader better contextualize the material. Finally, MJTL has provided us with a solid, straight-forward and honest (he signals it when he is speculating) tool which will undoubtedly facilitate further advances in the field.