BMCR 2005.12.09

Concrete Vaulted Construction in Imperial Rome. Innovations in Context

, Concrete vaulted construction in Imperial Rome : innovations in context. Cambridge: Cambridge University Press, 2005. xxii, 274 pages : illustrations ; 29 cm. ISBN 0521842026 $85.00.

A revised and expanded version of her doctoral dissertation, Lancaster’s work, as its title promises, concentrates on the origins, technique, and evolution of imperial concrete buildings in and around Rome. Her introduction (Chapter 1) begins with a definition: “Roman concrete or opus caementicum is different from what we think of today as concrete … caemen-ta means rough, unhewn quarried stones and refers to the rubble of fist-sized pieces of stone or broken brick that were used in the mortar as aggregate … more akin to … mortared rubble … than to modern concrete” (p. 3). Briefly mentioned, vaulting during the Republic achieved formal recognition with the vaults of the Tabularium (78 B.C.) and the Theater of Pompey (55 B.C.). An examination of the structural behavior of vaults leads to a consideration of the supporting Roman technical expertise characterized as: “experimentation on the building site and the understanding of basic geometrical principles” (p. 11). The extremely useful maps 3 and 4 accompany subsequent discussion of the materials and sites from which the ingredients of concrete came, and a brief discussion of the organization and history of Rome’s building industry follows.

The second chapter examines the evidence for the carpentry that shaped vaults and domes; the third, the mortar and caementa, the essential ingredients of Roman concrete. The next three chapters characterize the materials in vaults: amphoras (Chapter 4), ribs (Chapter 5), metal clamps and tie bars (Chapter 6). Chapter 7 assesses the stability of various vaults and domes. Chapter 8 examines the methods devised from the Renaissance forward to determine their structural integrity, and, with the aid of these concepts, evaluates the techniques of construction used in the Basilica Ulpia, the Pantheon, and the Temple of Minerva Medica in Rome, and the Temple of Mercury at Baiae. Chapter 9 summarizes the evolution of vaults and domes, discusses their social context, and explains their eventual disappearance in the later fourth century A.D. In the four appendices, Lancaster (1) describes the principal monuments cited, (2) lists building techniques at the sites discussed, (3) analyzes scoria (a light volcanic material similar to but heavier than pumice) at several sites in Rome and Pompeii, and (4) shows how thrust analysis may determine the structural stability of a barrel vault.

The study of Roman imperial concrete construction is not a new topic. Extensive treatments by Blake and Lugli have long been standard works, and, in the mid-sixties, MacDonald also focused chiefly on concrete buildings in and around Rome after the great Neronian fire of A.D. 64.1 In accounts of varying length, Blake and Lugli describe most of the important Roman sites in Italy for their stated periods. MacDonald concentrates on a few grand vaulted buildings in Rome: Domitian’s palace on the Palatine, the Markets of Trajan, and the Pantheon, and, while wide-ranging, his discussions of construction techniques are generalized. And yet, useful as these approaches are, they are very unlike those of Lancaster. A former practicing architect (in the six years prior to her graduate studies at Oxford University), she observes her monuments in close professional detail and arrives at novel conclusions.

Mortar improved significantly between the late first century B.C. and the second century A.D. Lighter caementa in the upper sections of domes and vaults lessened their potential lateral thrust. Brick linings on the intrados of vaults prevented wooden frames from adhering to the concrete after it had cured. Dependent on large scale production in the brick industry, these linings were in use for only about a century (between the reigns of Trajan and Caracalla). The brick industry declined precipitously in the later third century A.D. when political problems temporarily ended large-scale building projects in Rome. Vaults and domes—the products of the sophisticated wood-working skills (partially military in origin) that shaped their formwork—survived. They were the essential components of bath buildings, one of the commonest architectural expressions of imperial munificence, and remained popular into the early fourth century A.D.

By then, the increasing skills of Roman builders had noticeably altered architectural design. The simple barrel vaults of the platform of the Temple of Jupiter Anxur at Terracina (early first century B.C. [p. 5, ill. 1]) and the barrel and pavilion vaults of the Tabularium in Rome (78 B.C. [p. 5]) gave way to the triple cross vaults above the nave of the Basilica of Maxentius (A.D. 306-310), 30 m wide (pp. 137-138, 139 ill. 122) supported by buttresses on the roofs of the three barrel-vaulted rooms on either side (p. 36) and by the rooms themselves (with vaults 24.5 m wide). Supporting walls became thinner and more complex. In the decagonal nymphaeum in the Horti Liciniani (the “Temple of Minerva Medica”)—”an attempt to combine many of the preceding techniques into the most efficient package possible” (p. 147)—piers thinner than those in the Pantheon (pp. 97, 100 ill. 80, 147, 158-159)2 supported a ribbed dome (pp. 109 ill. 94; 110-111 ill. 95; 144, ill. 129; 161-163, figs. 142-143). Light caementa filled the sections between the ribs. Nine projecting apsidal chambers, “design element[s]” (p. 147), helped buttress the dome, but in four of these rooms (two on each side of the central axis) wedge-shaped corner piers and pairs of columns supported the exterior walls.

With ten generously proportioned arched windows in the sides of the rotunda and the openings between the columns in the apsidal rooms, the “Temple of Minerva Medica” also emphasized the Roman desire for better lighted spaces, a trend probably related to the invention of glass in the late first century A.D (pp. 147-148). While the subdued light in interior of the Pantheon comes only from the oculus in the dome and the entrance, in the “Temple of Minerva Medica,” light from the doors and windows (p. 36) must have brightly illuminated the marble veneer on the walls and the mosaics that originally covered the intrados of the dome.3 And while the architect of the Basilica of Maxentius was concerned with supporting the fabric of the vast groin vault over the nave, he also gave considerable thought to lighting. The facades of each of the three lateral, latticed-ribbed barrel vaulted rooms (106) had two stories of triple windows, while in the nave, the thermal windows under the lateral vaults and three amply proportioned windows at each end provided additional light.4

The organization of the book occasions only minor criticisms. Major discussions of buildings appear in a number of different places. On the Pantheon, see pp. 43-46, 62, 57-58, 100, 141, 143, 155-159, 192; on the Basilica Ulpia, pp. 118-125, 156, 190; on the “Temple of Minerva Medica,” pp. 78, 181-163, 201-202; etc. Illustrations of the Pantheon appear on pp. 44, 55, 62, 100, 101, 141, and 159; of the Basilica Ulpia, on 122, 123, and 157. Consequently, to recover the full treatment for each structure, the reader must review several locations. With all the conclusions and illustrations for each building in Appendix 1, the author could have spared her readers much work, and short citations throughout the text might have referred them to the appropriate section for each building in the appendix. Further, the discussions of the structures listed in Appendix 1 would be much clearer if each had a plan, and on these plans the author might have indicated precisely the areas she discusses. For instance, in her treatment of the Domus Tiberiana (pp. 186-187) she notes that, “The impressions of boards … are visible along the intrados of the Neronian vaults.” A plan should locate those vaults. And at least one illustration slightly misleads the reader. Necessarily taken at the level of the spring of the vault, the plan of the dome of the Temple of Minerva Medica (p. 109) does not show the openings with columns in four of the apsidal rooms (see above). Thus the unwary reader could visualize the building with a heavier, more closed structure than in fact it had. A second plan, the ground floor, would have helped explain the building better. Aside from such minor criticisms, however, Lancaster’s arguments mark a more sophisticated approach to the study of Roman architecture than has hitherto been possible. As she notes (p. 2), the recent publication of many individual Roman buildings encourages a synthetic study like hers, but her extensive on-site studies and simple but handsomely executed line drawings show us how and why Roman vaults and domes stand; how the Romans calculated the strength of their constructions; how changes in materials affected the stability and character of concrete buildings, and how developments in contemporary society determined these changes. She thus indicate why concrete vaulted buildings may have been so popular in imperial Rome (they were gathering places for large numbers of people [p. 168]), and why they disappeared after the reign of Constantine (the new Christian churches were more easily roofed with timber [p. 179]). The use of Lancaster’s work in conjunction with that of Mark Wilson Jones’ Principles of Roman Architecture should give English-speaking students a solid introduction to the design practices of Roman contractors and architects. Indeed, books like these move us from archaeological monographs on particular monuments (like Kjeld De Fine Licht on the Pantheon or Carla Amici on the Forum of Caesar) or broad general texts on Roman architecture (like Crema and Ward-Perkins) toward an in-depth understanding of what Roman concrete, marble-clad buildings were designed to do, of what they did, and of the way in which their successes and failures influenced generations of later architects.5


1. Marion Blake, Roman construction in Italy from Tiberius through the Flavians (Washington, D.C. 1959), Marion Blake and Doris Taylor Bishop, Roman Construction in Italy from Nerva through the Antonines (Philadelphia 1973); Giuseppe Lugli, La tecnica edilizia romana (Rome 1957); William MacDonald, The Architecture of the Roman Empire, I (New Haven and London 1965, 1982).

2. Mark Wilson Jones, Principles of Roman Architecture (New Haven and London 2000) 186-187.

3. Luigi Crema, L’architettura romana (Turin 1959) 631, figs. 835, 838; 634-635.

4. Ernest Nash, A Pictorial Dictionary of Ancient Rome 1 (London, 1961) 180-182. John Ward-Perkins, Roman Imperial Architecture (New Haven and London 1981) 426-428; Crema (above n. 3) 593 ill. 787.

5. Kjeld De Fine Licht, The Rotunda in Rome. A Study of Hadrian’s Pantheon (Copenhagen 1968); Carla Amici, Il Foro di Cesare (Florence 1991); for Crema and Ward Perkins, see above nn. 3, 4.