Cementitious building materials are amongst the oldest, and perhaps most culturally transformative, of the ingeniously mindful manipulations of raw materials by human beings. Arguably, the most culturally impactive transformation before the twentieth century involves the room-temperature chemical reactivity in aqueous medium of volcanically deposited, finely divided, microporous alkaline aluminosilicates (pozzolanas) with calcium ions, supplied by slaked lime, to produce Roman hydraulic cementitious mortars which set underwater — the subject of the volume under review.

The four principal authors of this exquisitely produced 327-page monograph — documenting their 2002–2009 Roman Maritime Concrete Survey (ROMACONS) study of Roman underwater hydraulic concrete and its engineering throughout the Mediterranean during five hundred years of Roman hegemony — have built substantially on their earlier (1980s) Caesarea Ancient Harbour Excavation Project (CAHEP), a pioneering study of Herod's celebrated Sebastos harbour (10–9 b.c.e.) at Caesarea Maritima. Indeed, in this present account of their seven-year successor study, the authors (with the assistance of six additional collaborators) have expanded their purview of underwater use of concrete into an extensive exploration of Roman maritime concrete engineering throughout much of the Mediterranean. In this densely-written volume, they have provided an exhaustive compilation of literary sources, underwater structural surveying, core samplings and modern analytical evaluations of the materials comprising the underwater breakwaters, moles, pilae and other engineered structures of Roman harbours.

This monograph quickly takes on the dimensions of a magnum opus (or perhaps of magna opera, since the chapters are written by different combinations of the principal authors). The constellation of a classicist-linguist cum archaeologist (John Oleson), a classical historian cum archaeologist (Robert Hohlfelder), an architect cum archaeologist (Christopher Brandon) and a geologist-civil engineer cum archaeologist (Marie Jackson) has provided a composite model for attacking on multiple, co-ordinated fronts the complex interplay of political, economic, geological, technological and materials science factors. A notable chapter by Oleson invokes substantial passages from classical written accounts, appearing in Roman and Greek literature from contemporary observers spanning the fourth century b.c.e. to mid-sixth century c.e. (amongst them Cato, Vitruvius, Horace, Virgil, Strabo, Pliny (Elder and Younger), Statius, Josephus, Suetonius, Apuleius, Cassius Dio, Faventinus and Procopius), to underscore the commonality of their observations and provide a contemporary framework for reconstructing the materials processing routes strongly suggested by the study's materials analysis of core samples performed on both macro- and micro-scales. Other chapters supply a comprehensive mapping of Roman ports (Brandon), a thorough exposition of Roman wooden formwork for underwater concrete construction (Brandon), and extensive analytical characterization of sea-water concretes, aimed at documenting their formulation and processing and provenancing their sources (Jackson). Hohlfelder and Brandon construct revealing narratives of the mounting of this seven-year research campaign, which investigated maritime sites from Portus, Cosa, Antium and Baia in Italy, to Ptolemaic Alexandria, to Pompey's eponymous Pompeiopolis on the Anatolian coast, with technical assistance and financial support provided by, inter alia, the CTG Italcimenti Group in Bergamo. The tedious underwater core sampling, carried out to drill depths well below surface-affected layers of the sampled concretes, has provided the first reliable ensemble mechanical properties measurements of these underwater concretes, though as Jackson correctly points out the principal attribute of these concrete accretions is not strength, but instead their mass and long-term cohesion. This reviewer applauds the team's informative attempt at an in-situ reconstruction of an underwater Roman concrete pila; three decades of laboratory-based teaching of archaeomaterials technologies have confirmed for him the revelatory benefit in reproducing ancient technologies for oneself.

Many of the findings and some of the data accumulated have been published previously in professional journals (sixty-one of their own published articles are cited by the authors), but never in such an integrated and cohesive narrative, nor as inclusively (witness sixty-six pages of data in four appendices). A significant, and somewhat surprising, conclusion from these accumulated data is that — in their construction protocols, materials and sources — the engineered underwater harbours of the Roman Mediterranean exhibit striking similarities and an apparent evolution; but even more curiously, all appear to have relied uniquely on a single preferred geographical source for the pumiceous volcanic-ash pozzolans used in Roman maritime concrete construction: the poorly consolidated volcanic ash deposits erupted from the Phlegrean Fields and neighbouring volcanic districts in the wider Bay of Naples region — the pulvis or pulvis Puteolanus of early Roman rapporteurs. The discovery of source singularity contrasts with the much wider range of alternative pozzolan sources and forms — such as the quarry sands (harenae fossicae) excavated from deposits in Latium, closer to Rome, and elsewhere — widely tapped for formulating hydraulic Roman concretes destined for use in terrestrial constructions throughout the Roman Empire after the first century b.c.e. The exclusive use of Baian pozzolanic material for sea-water concretes (in preference to local sources, such as the pumiceous ash of Santorini, far more proximate to those harbours surveyed in the eastern Mediterranean), may imply a Baian source advantage in conferring better underwater durability — or simply cultural inertia and the utility of Baian pozzolans as ship ballast that conveniently cushioned the amphorae cargoes in grain ships plying the Baia-Alexandria trade route.

The text is copiously illustrated, with some 383 figures (maps, drawings, photographs, often accompanied by paragraph-long informative captions) and fifty-one tables. But this is not a coffee-table book; far from that, this scholarly volume offers a delectable feast of primary- and secondary-source discovery drawn from decades of research into the underlying Roman history, politics, economics and social structures, Roman above-ground built infrastructure, Roman harbour design and underwater construction practices, raw components sourcing, Roman concrete science, geology of the Italian peninsula, vulcanology, Mediterranean trade and shipping routes, and sundry other related topics, with an enormous bibliography containing over five hundred references. A final postprandial reflection by Hohlfelder and Oleson offers up some appetizing implications of the study's well-digested conclusions.