Z.’s own final words (p. 379) splendidly capture the most consequential points of this important book (I have added emphasis): ‘The artes have come down to us, like so much else from Greek and Roman antiquity, as the scattered fragments of what was once a brilliant whole. The proliferation of knowledge in the modern age, and the consequent drive toward specialization, have not been kind to this Roman ideal of polymathy. Distant as we are from ancient life, we find it strange that so many and such varied facets of knowledge could have once been joined together, crystal-like, in polyhedral unity – the many aspects of an ancient prism through which the Roman understanding of the world was reflected. It is my hope that this book has fitted those fragments together well enough that we can once again hold that prism to the light and, chipped and roughly joined as it may now be, catch a glimpse again of the world as the Romans saw it’. It is one thing to sense the ancient Romans not handling many an issue in quite the way in which we moderns would be inclined to approach the same matter. It is surely another thing to take this (often inchoate) awareness earnestly and then to apply that more acute recognition. It is in this regard, especially, that Z. excels. How, then, does Z. go about reassembling a holistic Roman cosmos of thought and understanding?

The first step (Chapter 1) isolates what Z. calls the ‘higher artes’, i.e. areas of specialised knowledge to which a member of the elite might devote time and attention – say, agriculture, as opposed to cobbling. He then (most crucially) offers a fundamental characterisation of these zones of endeavour. Z. does not dwell on an attempt to delimit which disciplines might have qualified as the artes, given that the Romans themselves never forged anything like an unambiguous canon. In any case, Z. finds such higher artes to have been typified by four most essential features, which they shared and which consequently placed them into a principally unified world of thought. Any proper ars was (1) systematic; there was a ‘systematic and logical organization of the contents’ (p. 19) of the field of expertise. That said, Z. recognises the fact that any given Roman author writing (about) an ars might well ‘balance the utility of logical organization with other literary, didactic, and philosophical concerns’ (p. 22). The to-and-fro in this respect emerges plainly over the course of the book. These artes were typically (2) interdisciplinary; they were closely tied to one another by virtue of their working principles and methods, which made the artes into ‘discrete but related domains of intellectual inquiry’ (p. 26). Then, there is the matter of (3) explanation, ‘the notion that technê or ars entails an explanatory knowledge of its methods in terms of natural causes’ (p. 26). Z. recognises that this standard does not apply universally to the artes examined in the book; however, he argues that a vision of the connection of most artes to the natural order of things was more important during the Roman imperial period than has generally been recognised by modern scholarship. Finally, Z. talks of (4) balance in the artes: ‘the demand for theoretical knowledge was tempered by the imperatives of practical experience’ (p. 31). While each of the four concerns adumbrated had roots in Greek thought, it was the Romans, in the late republican period (esp. Cato, Varro and Cicero), who drew these premises together, so as to form something like a ‘coherent vision of ars’ (p. 36). Z. then suggests that the integrity thus imparted to the fundamental concept of the artes caused these disciplines to surmount mere pragmatism and thereby to comprehend the world – nature, knowledge and society. Nonetheless, ‘[t]he artes were not univocal, since their intellectual unity derived basically from a set of shared questions or concerns, and only secondarily from shared answers’ (p. 207). A second chapter argues in more detail that, with the arrival of the imperial age, the artes grew into ‘as much an epistemic as practical paradigm of Roman Empire’ and that ‘[a]n absorbing interest in Empire encouraged Roman authors to present the universalized ways of knowing and doing that belonged to their artes … as specifically Roman ways of knowing and doing’ (pp. 76–7). In short, the book examines Roman methods of knowing rather than what is ultimately known.

The rest of the volume demonstrates how all these points shaped depictions of various artes – and how those depictions should therefore be perceived as kindred in terms of their thought world. Z. examines: Vitruvius, De architectura; Columella, Res rustica; Celsus, De medicina; Onasander, Stratêgikos; Frontinus, Strategemata; and finally, the ars mensoria, as chronicled by Frontinus and Hyginus. At the heart of Z.’s investigations lies this: ‘A basic contention throughout this book is that we can only understand the artes if we read the self-conscious reflections of the prefaces with and against the technical and didactic contents of the works’ (p. 99). Z. sticks fundamentally to this approach. He selects a section, or sections, of a work and then subjects this piece of writing to punctilious analysis with respect to the four issues delineated above. This allows an exceptionally precise view of the manner in which Vitruvius, and the rest, constructed the thought world of their artes. Indeed, this approach reveals a kind of disputatio communis among these areas of investigation. This aspect of Z.’s book is especially momentous. For once one realises that (a) any Roman who tackled any given ars was presumably operating in the ways laid out by Z. and that (b) these same individuals imagined themselves as belonging to a community of disparate investigators who were all working similarly and who were thus enmeshed in a communal dialogue as to the manner of scientific inquiry, the potential significance of Z.’s argument increases exponentially.

Let us pin that claim to one Latin term/concept: ratio. This is ‘perhaps the most conspicuous thread running through this book’ (p. 372); ratio is also ‘a complex and polysemous notion’ (p. 239), with meanings (in keeping with Z.) such as ‘theory’, ‘method’, ‘reason’, ‘account’, ‘principle’, ‘calculation’ or ‘reckoning’. Most crucially, ratio is typically involved when theory and practice collide. Thus, in the world of surveying (pp. 340–71) there is a notional ratio caeli/mundi – a conjunction of natura, veritas and ratio – that ought ideally to govern the constitutio limitum. This (theory), however, must somehow be accommodated to the ever-present possibility of local custom – usus or consuetudo (i.e. ‘habitual practice’). Let us now move beyond the covers of Z.’s book. In 4 ce Lucius Lentulus abruptly contrived a novel type of codicil. Was the invention allowable, or was it not? Augustus convened the lawyers and asked (Just. Inst. 2.25 pr.) ‘whether this could be accepted, or whether this use of codicils was contrary to the ratio of the law (iuris)’. Trebatius Testa found that Lentulus’ codicils violated the ratio iuris; still, he thought that such a codicil might be accepted since ‘this would be extremely useful and necessary (utilissimum et necessarium) to the citizens’. In short, legal theory (ratio iuris) and potential practice (here, utilitas) collided. A scholar of Roman law might be inclined to view this juxtaposition purely in terms of law and Roman legal reasoning. Z.’s book shows us plainly that such an approach is surely blinkered, and badly so. Put simply, we should not allow ourselves to isolate the thinking of Augustus and Trebatius from that of Frontinus and Hyginus; and the results, if we listen to Z., are likely to be considerable.

Z.’s book is important for what it does. It will be equally important for many things well beyond its own purview. The volume is not light reading; but that must be weighed against the fact that it does some very heavy lifting.