BMCR 2003.11.20

Roman Builders: A Study in Architectural Process

, Roman builders : a study in architectural process. Cambridge: Cambridge University Press, 2003. xvi, 303 pages : illustrations ; 26 cm. ISBN 0521803349. $25.00 (pb).

Rabun Taylor (T) states in his introduction: “This is a study of the realization of architecture … the cultural and cognitive processes involved in the act of creating buildings.” T’s methodology is to present “a roughly logical sequence from the planning stage to the final decoration” but not to limit himself “to a single narrative… rather … to find the essence of each distinct procedure wherever it presents itself”. That is, he does not follow a single building from planning to completion but draws upon exemplarly examples of specific procedures from several buildings. T’s book is then unlike other volumes on Roman architectural methods and processes, which are encyclopedias of methods, techniques and materials.

T’s presentation is in the form of an introduction and six chapters. Chapter 1, “Planning and Design”, is a helpful primer on such subjects as Vitruvian principles, statical indeterminacy and the difference between arithmetic and geometric proportions. As important as is his discussions of the basics of design is T’s comfort with the mathematical and theoretical. His interest in structural mechanics and theory is revealed not only by illustrated examples, e.g. the consequential redistribution of forces by the addition of a tie rod to an arch, but by the relative length of such discussions: the longest subsection is Structural Innovation In Design, a section where he can discuss and illustrate just such interest.

Chapter 2, “Laying the Groundwork”, brings the building from the translation of plan to site and from foundation to the ground-level floor. In addition to the basics of foundations, hypocausts and floors, T includes discussions of two topics often overlooked or minimalized: 1) the difference between idealized and realized plan and 2) internal water supply and drains.

Chapter 3, “Walls, Piers, and Columns”, presents those architectural elements best known and most commonly discussed. T’s exposition is good up until we get to issues of hard lifting, i.e. raising stone elements, especially those of colossal size. How the Romans maneuvered colossal columns into position is not known for certain, and accordingly T must rely more upon deduction and theory, both his and those of others. This process, in turn, leads T to posit a theory to explain the revised column height of the Pantheon porch.

T’s solution for the Pantheon porch is based upon a simple fact and two premises. The simple fact: the need to reorient the column shaft from the horizontal required for transportation from the quarry to the vertical of its final position. The two premises: 1) tilting the shaft required a device built specifically for this task and 2) the Pantheon architect(s) planned poorly. T embraces the hypothetical tilting mechanism of Jean-Pierre Adam’s invention (shown in T’s fig. 56). Adam’s mechanism is not unreasonable and it is consistent in part with the crane depicted in the well known relief from the Tomb of the Haterii in Rome. The secondary system of pulleys and lines depicted in the relief were clearly used to hoist the crane and once the crane was vertical could have been used as guy lines until the load was positioned and set. What is not clear in Adam’s illustration, as noted by T, is how the shaft, once vertical, was released from the cradle without crushing or chipping the base of the shaft and without bending or breaking the empolia. This is where the primary block and tackle of the Haterii relief could come into play, just as it is depicted in T’s Figure 54, a line drawing based upon a funerary relief from Capua. This block and tackle was not designed to pivot from horizontal to vertical, as were the secondary systems, but served to hold, lift, and lower vertically. Adding this to Adam’s scheme and assuming a collar at or near the upper end of the shaft to provide purchase and the control necessary would offer the necessary means for the final placement of the shaft, including alignment of the empolia. With or without the addition of a primary block and tackle, was Adam’s hypothetical cradle employed in the Parthenon porch? It is impossible to say, but I would hazard that other solutions are more likely both for the porch and for raising colossal columns in general.

T’s theory for the Pantheon porch assumes that Adam’s mechanism was used and that the architect was incompetent, distracted, or both. The later follows if Adam’s mechanism were the lifting system used. That is, the configuration of the porch, as recognized by T, did not provide the necessary space for Adam’s machine to pivot a shaft 50 Roman feet (RF) long. T’s conclusion: shorter columns were used to accommodate the machine. The only secure conclusion here, however, is that Adam’s machine could not have raised shafts 50 RF high in the Pantheon porch. To suggest that the architect did not discover this until it was too late to change the configuration of the porch assumes a level of incompetence that is manifest no where else in the building. Yes, it is common practice today in architectural firms for junior members to design the more straight-forward components, bathrooms, lavatories and stairwells for example. And, by analogy, it is not too great a stretch to assume such practice was common in antiquity. But, to assume that either the “A level” team was so preoccupied with the construction of the cylinder and dome of the rotunda that they missed so great an error being committed in the porch or to assume that the same architect who designed and oversaw the construction of the rotunda failed to plan adequately on how to raise the columns of the porch is quite a stretch.

There is no certainty at all that Adam’s lifting cradle was the device used in the Pantheon porch. In fact, there is direct evidence that another equally successful method was available and one that did not have the same spatial constraints as Adam’s. Roman architects had great confidence in their ability to move and hoist huge loads. Shafts the intended height of the Pantheon, 50 RF, were raised during the Hadrianic period in Rome at the Temple of Venus and Rome and apparently at the Temple of Divine Trajan. Shafts 50 RF long would have weighed ca. 100 tons. Loads this great were lifted with the cornice blocks and set at a height even greater than the Parthenon porch in the Temple of Jupiter at Baalbak. Granted a cornice block did not have to be rotated 90 degrees from horizontal to vertical. This did not, however, negate the need for controlled lateral movement. That such temples as Jupiter Baalbek were built is testament to the fact that the machines necessary to move and position such huge loads to such heights did exist and were used with success. Were such machines also capable of righting colossal columns? There is no reason why they could not. Although there is no way to tell scale in the relief from Capua, it does appear that this is the very maneuver depicted. This same maneuver, as well as controlled lateral movement after the columns were hoisted, is a given in the erection of the columns in level 4 of the Colosseum according to T’s fig. 96. In sum, it would seem better to look for a solution to the problem of the Pantheon porch that was not predicated upon a hypothetical machine and the incompetence of the architect(s).

Chapter 4, “Complex Armatures”, is a forty-page case study of the Colosseum. This is offered as a plausible but not certain account of raising the structure from ground level to peak. In spite of being something of the antithesis of T’s professed goal in the introduction (i.e. it is a continuous narrative of one structure), the overall reasoning is sound. Although I do not agree with every detail of the sequence of events (e.g. I suspect the vaulting at level 3a would have been completed before stacking the piers of level 4), this chapter may be the best of the book.

Chapter 5, “Roofing and Vaulting”, is as the title suggests in parts. T begins with vaulting and focuses on centerings, issues of their mechanics and their design. Semi-circular and arcuated trusses came to be the Roman solution to roofing open spans. Their application and form became increasingly complex as the width of the span increased. T avoids getting bogged down in formulae and overly detailed presentation of theories and in so doing provides a coherent summary. The subsection on vaulting acts as a preliminary for the twenty-one page discussion of the construction of the Pantheon dome. Here again the emphasis is on the centering, rightly so given T’s emphasis on process. T presents the theories of three other scholars before offering his own, one that denies the use of a central tower and advocates the use of flying trusses held by exterior cranes. T’s solution is based in part upon denying that putlogs were employed in the construction of the dome. This premise is used to discredit the scheme devised by Viollet-le-Duc in 1875. T asserts that the putlogs indicated in Viollet-le-Duc’s scheme are an impossibility because such putlogs could not have been extracted from the dome once set. This is incorrect. Sockets for putlogs are no more excluded in a dome mold than are coffers. Evidence for the presence of putlogs in the Pantheon dome is indeed present in the photograph taken in 1898 of an interior segment of the dome stripped of its plaster, T fig. 117. On the right rib of the middle coffer of the three stripped of their plaster about three-quarters the way up from the cornice is a socket for a putlog. This socket is off from horizontal by ca. 18 degrees. This was not due to careless placement of workers in 1898. The impressions of the shuttering used when the dome was first poured are visible both above and below the socket. They too are off horizontal by the same degree as the socket. This shows that for whatever reason the putlog and shuttering slipped or were torqued ca. 18 degrees off horizontal before the dome was poured and this aberration was preserved in the impressions left in the concrete.

There really is no way of telling whether or not the dome trusses were of two segments, as T hypothesizes. I am not sure how making the necessary assembly and disassembly of a truss in two segments half way up the side of the dome would be any easier than positioning a unibody truss. Furthermore, whatever the configuration of the truss I believe it more likely that the main bracings would be placed opposite the thickest part of the dome, i.e. the ribs between the coffers, as Viollet-le-Duc envisioned, and not in various places opposite the coffers as T has it.

Chapter 6, “Decoration and Finishing”, discusses the end of the construction process, with little room for principles and theories. Rather, it is practical experience that guided the artisans, and it is practical experience or understanding of these issues that is most beneficial to scholars. This chapter is the low point of T’s work, mostly because it reads as if he felt he had to write about these topics. Many are dealt with in a cursory fashion: plaster, fresco and stucco are given five paragraphs; floor mosaics, five paragraphs; wall and floor veneers, four paragraphs. Granted the concern is about process, but T moves here with uncharacteristic speed. Where T seems most interested is in those instances when he can theorize on technique. The results are not always satisfactory. Rather than relying upon a complex, mutli-tasked approach to problems, we can assume Roman workers acted much like their contemporary counterparts, for example, a plasterer laying out parallel, perpendicular, and radial lines will look for the simplest means to produce the desired results. Methods for siting a specific point or line relying upon multiple transfers from plumb bob to carpenter’s square will soon give way to quicker and more elegant methods. Parallel horizontal lines can be quickly drawn by using lath as a guide to connect two points of equal height, and points could be rapidly set by a plumb bob and rule. That same lath would be pliable enough to follow the curve of an arch, vault or dome to connect equidistant points on parallel horizontal lines and provide parallel vertical lines or radial lines. This is, in fact, how contemporary tilers address similar problems.

In conclusion, I admire what T has set out to do and have enjoyed reading most of this book, in spite of the occasional prose I would never dare write. His penchant for digesting theory and principle and explaining them carries him far. What seems to be a lack of practical experience, however, is his undoing. For as with the porch and dome of the Pantheon, when faced with problems without a clear solution, T’s reliance on the theoretical leads him to use fancy where solutions based on common practice or known techniques would be more certain.