Proceedings of the First International Congress on Construction History, Madrid, 20th-24th January 2003, ed. S. Huerta, Madrid: I. Juan de Herrera, SEdHC, ETSAM, A. E. Benvenuto, COAM, F. Dragados, 2003. Foundations and wall structures in the basement of the Colosseum in Rome Heinz Jürgen Beste Following a generous offer made by Rome' s oriented in the East-West direction, and this is also Archeological Superintendence, the German true for the greater part of the walls one finds there. Archeological Institute in Rome commenced an These walls, made of tufa blocks and bricks, investigation of the construction details of the arena subdivide the basement into twelve corridors of and the basement of the Colosseum in 1996. The different widths and lengths and, more precisely: six Colosseum forms part of a series of well preserved elliptical corridors that run parallel to the encircling major structures of antiquity whose state of wall and nine corridors parallel to the longitudinal preservation is inversely proportional to our axis (fig. 1). knowledge of the history of the building.' The ultimate aim of the work we have commenced is to distinguish the multitude of building phases that PHASE 1 followed each other in the five centuries in which the world's largest amphitheatre was in use.2 Moreover, it At the beginning of our investigations attention was is proposed to attempt design reconstruction based for concentrated on distinguishing the individual the first time on a thorough cataloguing of building building phases and, more particularly, the tufa walls, details and history. The Superintendence also expect because these divide the basement into the a proposal for using the basement as a museum, as aforementioned corridors. For this reason I shall also for the restoration of the arena floor. henceforth describe these tufa walls as Phase l. As The basement of the amphitheatre, which several reconstructed on the basis of our building records, walls subdivide into a series of corridors, measures this phase is characterized by a very light but long- 76.12 m along the longitudinal axis of the oval and spanning construction. The walls, which are about 90 about 44.07 m along the shorter transverse axis. It is cm wide and 6.30 m high, attain arch spans of up to delimited by the so-called encircling wall, which in 4.0 m. These filigree walls made of tufa, which are set its day carried the podium. Constructively this wall is between 2.0 and 4.0 m apart and carried the wooden the counterpart of the so-called foundation wall arena floor, were presumably at first underdesigned which supports the outer facade. If one today for withstanding the vibrations caused by approaches the edge of the arena from the stands, one earthquakes, ground subsidences and perhaps the looks down at the basement, because the wooden games themselves and therefore had to be arena floor has long since disappeared. The subsequently stabilized, as is clearly brought out by longitudinal axis of the oval-shaped basement is our findings (fig. 2). 374 H, J, Beste Strutturaintravarllnonella fondaziOne del CQIoaeeo Sb'uttunil in tufo negUípogei - =~~~":'=~O --- SlnItturalnmeltonJ I ¡ I ~..".;';-."'_::- "' ~. .,."..;." s'c .:',.;...-" -" . .f - j .,.',. ..- -'- ""w, ''''. ... " ""' ...,"~.'~"~.a.&~~~,"',.;, r:iií \ lit .h ~C"''''''''-'''''-'_.' " - '" ,_:::~.T'~;:::';'-:'" :;' ., ~...~~~i¡:',r;;~~~~'", -......... ¡ . "'::: ':¡;:i:::::::-:-~..,. ¡ , ~":' --:~.. -'o, ~ o 5 10 :10 040 &1 __.TO 100 20" --_so .. !lO Figure I Foundation pIatform and basement of Colosseum, general site plan PHASE 11 which 1 believe functioned as the piJe holes for this walL For reasons of construction the walls 4 and l 1 For this reason all the openings in the arches were could not have been built at a later stage as they reduced by inserting brick arches 60 cm deep within support walls belonging to phase IlI. the existing ones. What is particularly noteworthy about this work is that the soffit was covered with sesquipedales and bipedales, thus making it possible PHASE III to use falsework instead of complete centering. At the same time as the arches were consolidated, all the This phase consisted of stabiJization involving all the openings and passages were narrowed by providing walls. It repeated the procedure of phase II by adding each soffit with a strong brick pillar (c.60 x 60 cm). masonry in all the passages, which were thus further The only reason why we assume that the walls reduced in size. The tufa walls in corridors e, E north, numbered 4 and 11 belong to phase II is that they are E south, G north and G south were each reinforced by made out of brickwork with a basic tufa layer. 1 the addition of brick walls rising to a height of c.3 m; suppose therefore that in phase 1 there may have been they were joined to each other by means of transverse wooden piles instead of the walls 4 and 11. There are arches and thus gave rigidity to the original walls numerous square structures in the basic tufa layer (fig. 3). Foundations and wall structures in the basement of the Colosseum 375 Figure 2 Reconstructed scheme of the basement, Phase ] PHASE IV The state of research of modern times reflects the lack of interest of the classical authors. Every Phase IV constituted a very substantial alteration of description of the building speaks of the foundation the existing subdivision of the basement because it and the manuals do of course provide an summary involved the erection of a brick wall (c.2.3 m high) in overview of the various solutions, but fight shy of a corridors F north and F south that closed off the true analysis of the problem.4 Though the foundations greater part of the passages that served them. This are literally fundamental for every building structure, phase is distinguished from all the others by the fact only a few papers have hitherto been dedicated to this that it does not consist of bricks of uniform size and theme.' And this notwithstanding the fact that some rests on a pediment made of material that must ha ve classical authors speak of building failures during fallen down from the top of the walls. construction due to inadequate foundations.6 Theoretical treatises about technical details or The fact that the 1'oundation is the sole part of a traditions regarding the design and dimensioning of building that cannot be designed by means 01' foundation are not to be found in the literature of permanent correcting trials during construction shows antiquity. Vitruvius, who provides us with quite a few us that the problem must be considered to have been constructional details, dedicates a brief subchapter to solved in the case of the monuments that are still the theme, but never really comes to grips with the standing today. Although considerable interest has problem.3 always been shown in the structural concept and the 376 H. J. Beste Figure 3 Reconstructed scheme of the basement, Phase III static safety of the Colosseum, the state of our arches, while the space between them has been knowledge about the foundations of the building is backfilIed with soil. very scant. 7 Presumably the surviving ancient For a long time the theory formulated by Cozza structures and especially the Colosseum suggest a about the structure of the Colosseum's foundations stability and durability such as to make us tacitly was neither doubted nor checked, and it was on]y in assume that they are adequately founded. 1977 that a trial boring executed in the area of the In his book entitled Ingegneria romana( 1927), outer circumference showed that the foundation Giuseppe Cozza was the first author to consider the consisted of opus caementicium, and not opus problem of the foundation of the Colosseum. quadratum as had previously been assumed.x According to his concept, which he developed in the The reconstruction of the arena floor commenced light of the structure of the eastern gallery (38), the 80 in the year 2000 brought with it the possibility of walls that carry the roughly 50 m high superstructure sinking six sampling cores in the basement to cIarify and cavea of the Colosseum do not stand on a the foundations on which it rested. Three of these foundation platform, but rather on strip foundations were situated in walls 7, 8 and 13 (S 1-3) and a fourth made of opus quadratum, each roughly 3 m wide and in corridor H (SA). A further trial boring was carried reaching down to a depth of about 6 m. In order to out in niche 39 (SB) and yet another (SC) between assure a solid support and thus enhance their carrying niches 15 and 16. The latter, however, was horizontal capacity, these eighty strip foundations -in the rather than vertical (fig. 4). opinion of the author- are joined by transverse The results of borings SB and SC, considered Foundations and walJ structures in the basement of the CoJosseum 377 ea +9001 +8¡.oQ..sin1 a 80&110 di fondazione C8. +22,00 ~ +9.00 I +8,00 slm g~ b muro di contenlmento intemo ~ ea. +22,00 ~ +15,50 $1m h~ ¡pagel e fondazione ¡pogel (US 635) ea. +15.50. +12,901 +11.35 slm i galleria probabilmente funzionale al cantiere ea. +16,20 slm f muradi cantenimento eslemo ~ ca.+22.00~ +16.00slm ~ 20 30 40 50 60 70 Figure 4 Section through the shorter transverse axis from the CoJosseum together with those of the 1977 trial, made it possible of view, the fact that different techniques were for the first time to make some concrete statements employed for the two sections means that the lower about the construction process and the size of the section must have been built below ground level and foundations.