Masonry Constructions as Built Archives: An Innovative Analytical Approach to Reconstructing the Evolution of Imperial Opus Testaceum Brickwork in Rome Gerold Eßer Vienna University of Technology, Austria The Colosseum, Trajan’s Market, the Baths of buil dings are to be regarded as the outcome of Caracalla and the Basilica of Maxentius: the monu- rational decisions made on the basis of economy, mental ruins of the imperial representational build- durability and functionality. Particularly in the ings mark the crystallisation points in a profound, area of important imperial public buildings, where centuries- long recasting of the appearance of the the pressure to be successful was exceptionally city of Rome (Fig. 1). The cores consist of practi- high, the conditions imposed by the market were cally indestructible opus caementitium, faced with certainly strictly observed. Large imperial buil- hard, quasi- industrially produced fired bricks. This ding projects in which often many thousands of construction method, later called opus testaceum, workers had to be organised and directed required was uniquely suited to surviving the passage of the definition and implementation of standards time. For us today, this means that we have at our applicable right across the site. To ensure the suc- disposal an extraordinary wealth of evidence for the cess of a major project these standards had to be building construction methods used in those times. laid down in series of technical regulations. The Given that even the building sites of classi- doctoral thesis on which the present paper is based cal antiquity were subject to market forces, the examined the extent to which the organisation of large building sites influenced masonry construc- tions and whether, using the characteristics of the masonry that will be defined below, this influence can be read as a regulative on the erection of the structures. The question of chronology The existing methods of dating differ greatly in their precision and reliability. Scientific methods based on the examination of construction materi- als taken in situ from buildings focus on analysing phenomena and processes peculiar to the material character and composition of the building materi- als. As a rule they should all be approached with caution as regards dating: in many cases their dat- ing relates to the time when the material exam- ined was made and not directly to the period Fig. 1: Basilica of Maxentius in Rome, 306-312 A.D. during which the building from which the mate- 1158_Gerold_EBER.indd58_Gerold_EBER.indd 1133 007/06/20127/06/2012 114:36:524:36:52 14 Technology / Foundations & Masonry rial was taken was erected. Here, precisely, lies the tain accepted limits. Consequently strategies must great appeal of dating- oriented analysis of brick be developed that define and describe the essential masonry constructions: in comparison with build- aspects of this enormous range of findings. ing materials, masonry structures form so to speak the next, higher step in the process of creating a building. They are the building itself, or at the Present state of research very least its essential and innermost core. If we can exploit this characteristic to arrive at a dat- The number of important contributions to the ing, then our results will reveal, very closely and dating of urban Roman testaceum brickwork is directly, the point in time when a historic con- not very large. The first and original attempt was struction was built. published in an article by the American archaeolo- gist E.B. Van Deman (Van Deman 1912), which Problems in dating brickwork appeared in two parts. In a concise work based on If we view brickwork constructions as systems that, an enormous knowledge of antique monuments with their variations on an ideal model, practically gathered over a period of decades, the author suc- make up the entire volume of a building, then ceeded in producing a first classification by epochs we are confronted with an extensive and complex of caementicum constructions within which brick- range of findings (Fig. 2). Not only can brick- faced masonry structures form the most important work structures be read as the standard surface of category. In her analysis of various masonry typol- a closed wall; they also display a variety of con- ogies and epochs, the author develops a nomen- structional details and with their core penetrate the clature to describe the characteristics relevant to third dimension of walls. Even if we succeed in fix- defining a chronology. ing in time the canon of constructional possibili- Thereafter the most important publication has ties of a certain building tradition on the basis of been G. Lugli’s major work on Roman construc- all the different variations used, the human inad- tion technology with its often lexically meticu- equacies of those who carried out the work will lous description of the technical aspects of Roman still result in variations on this canon within cer- brickwork (Lugli 1957). Today’s experts are some- what critical of his attempts, on the basis of just a few characteristics, to fix the dates for the vari- ous typologies of Roman brickwork structures. A quarter of a century later the work by T.L. Heres, Paries: A Proposal for a Dating System of Late- Antique Masonry Structures in Rome and Ostia, introduced an improved system of documenta- tion into the discussion on methodology (Heres 1982). However, this work has a serious flaw in its method: although dated and undated masonry structures are distinguished from each other, the reader is left unsure whether and on what basis given datings are accepted or questioned, and how the dating system presented, which ultimately seems to operate on the basis of intuitive compa- risons, can be used to anchor buildings securely to a particular point in time. A number of subsequent works (Giuliani 1990, 19- 24; Cecchelli 2001) clearly betray reservations about the known masonry- based dating meth- Fig. 2: Mausoleum of Helena Augusta, 320-325 A.D.: Typical ods. M. Cecchelli, for example, in her informa- late antique testaceum brickwork, area showing the stand- tive and well- structured catalogue section on early ard bond. 1158_Gerold_EBER.indd58_Gerold_EBER.indd 1144 007/06/20127/06/2012 114:36:544:36:54 G. Eßer / Masonry Constructions as Built Archives 15 Christian masonry, restricts herself to compiling photographical, in part also photogrammetrical, and documenting all data of relevance to the buil- documentation of representative sections of the ding structures, ranging from the historical sources brickwork, a procedure was developed that com- through details of research history to examinations bines a series of new processes from the fields of of masonry structures following a strict standard. surveying technology, computer science and sta- A breath of fresh air was introduced into the tistics with the familiar methods of recording and discussion by a research direction that has been evaluating masonry data. It produces results that developed with remarkable success since the 1970s allow masonry structures to be characterized in a under the name mensiochronology, which analyses differentiated and objective manner. dimensions and uses modern statistical methods to evaluate mediaeval and modern bricks (Fossati Photogrammetry 1984; Mannoni and Milanese 1988). Although In the course of the study it proved possible to hardly any note has as yet been taken of it in show that the use of tacheometric- assisted meth- classical archaeology, this interdisciplinary ini- ods of planar image rectification and cylindrical tiative has in many parts of Italy already pro- development (Fig. 3) allow entire areas of brick- vided numerically substantiated proof, based on work to be surveyed and documented, true- to- the economics of construction, of a direct con- scale and with the real colours. For the first time nection between the dimensions of the bricks exa- in the history of the comparative examination of mined and the time when they were made. brickwork, these methods also allow the numeri- cal recording and analysis of entire walls as con- structional systems. As well as being able to be Aim of the study used at different scales, ranging from detailed to general overview, the plan material produced The challenging aim of the study is to reconsider in this way allows larger areas to be dealt with, the problem of determining the chronology of spe- improves the statistical basis of the recording of cific examples of antique urban Roman brickwork data, and increases the transparency and verifia- – a group of examples of testaceum brickwork from bility of the entire documentation. the period between Diocletian and Constantine1 that have already been given fixed dates using other methods – under new methodical preconditions and asking different questions. Comparison of the samples of brickwork examined demanded strict selection based on the following criteria: belong- ing to a single region, having been commissioned by comparable clients, use of the same masonry techniques, and reliable dating. After all, only if we prove that the assumed development over a contin- uous period of time did in fact leave a recognisa- ble mark on individual buildings can we justifiably attempt to put hitherto inadequately dated brick- work into a proven chronological order. Documentation standard for testaceum brickwork Taking into account existing methods that com- bine a verbal, qualitative description of the Fig. 3: Baths of Maxentius on the Palatine Hill,