I recently made a weekend trip solo down to Rome. It was an adventure, complete with getting off at the wrong train station, missing my connection, being taxied to the wrong hotel and at one point getting my backpack stuck in the door of the train. I really should not be let out alone. Since I was in Rome for a conference, I didn’t have the opportunity to see much, but I did make it to the Colosseum on my way out of Rome (in fact barely made the train back. Adventure!)
The Colosseum, despite only retaining approximately a third of its original material, is still an impressive site to behold. The approach, so carefully considered to give the viewer a sense of awe, has been diminished but not utterly destroyed. The Colosseum was built by the Flavian emperors, Vespasian and his sons Titus and Domitian, who were rulers after Nero. While now painted as an excessive villain whom the plebians (or common folk) despised, it is uncertain if Nero was truly unpopular during his rule. However, Vespasian and his sons benefitted from a policy of blaming Nero of any and all woes in the empire. By presenting themselves as “rebuilding” Rome, which included doing away with Nero’s supposedly resented opulence, they could hope to win the people over. Whatever altruistic intentions might have governed their rule, restoring the “stripped” Senate authority and completing public projects for the common good were certainly pragmatic ploys. And so they commissioned and completed a great amphitheater “for the people to enjoy” built squarely in the center of Nero’s former Domus Aurea (Golden House), smack dab where his personal lake has been- a highly visible project which served their PR purposes very well.
Roman construction projects began with floor plans, scale models and various design sketches for the artisans involved. Roman design relied heavily on ratios and numerical patterns. The debate over how and why Romans favored which ratios, patterns and shapes is still rather fierce and technical. Technicalities aside, the Colosseum, some 190 by 155 meters (620 by 513 feet) was completed in 10 years- a rather short construction period for such a grand structure. Those with experience in project management can well imagine that a systemized approach must be at play. Peter W.G. Morris points out in his book The Management of Projects that contracts for such large public projects at this time were similar to our own, with descriptions of work, specifications and even negotiated methods of payment. This type of “secular” focus would disappear in medieval Europe when cathedrals and other sacred buildings (which most large projects at the time were) of much less grandiose proportion could take decades. Because of differences in construction details between the four quadrants of the structure, archaeologists have generally agreed that four different contractors worked on the Colosseum. While slave labor surely played a role in the construction, the skilled craftsmanship involved and the number of workers needed to complete such a project demonstrates a vast and trained workforce.
The planning that went into draining, excavating, creating a foundation and a site plan for the large amphitheater is extensive. Some 33,000 tons of soil were removed from the lakebed, and drains were installed 8m (26ft) beneath the foundations to divert water. The removed soil was used to raise the surrounding ground level nearly 7m (23ft) from its original elevation, perching the Colosseum above the surrounding valley and making it appear even grander upon approach. The foundations were built to support the huge weight of the structure in the clay soil. At the perimeter, the foundation walls built of brick and Roman concrete were 12-13m (39-42ft) deep, while the footings under the interior walls and seating were only 4m (13ft) deep.
By building the travertine ground floor, then placing travertine pillars along the radial walls, contractors were able to build arches of concrete and brick connecting the pillars. The minor pillars and walls of volcanic tufa were infilled afterwards. This system allowed for overhead coverage of the ground level but also provided ample space for moving materials between the ground and second level- meaning that workers could be building on both levels simultaneously. Once the structure was completed with travertine, tufa and concrete, marble was used to clad the exterior, as well as for creating seating, drinking fountains, statues and other ornaments. The Romans actually provided specifications for these marble pieces, which were mass produced off site then installed. This method of construction would have functioned much like the process of building skyscrapers today, where a steel frame is constructed quickly and the exterior skin and interior partitions are added afterwards.
A note on Roman concrete- at the time of the Colosseum’s construction, concrete was still considered a new and untested material in the capital. This would account for it being used only for the ceiling vaults and to bind the foundation bricks, and not as substantial load bearing members. Recent international investigations into Roman cement, the binding agent in concrete, have compared it to the modern Portland cement. The investigation revealed that the composition of Roman cement from lime and volcanic rock binds better, demands less heat (and therefore less carbon dioxide production) and lasts longer than modern cement mixes. It will be interesting to see if this and other investigations lead to any revolutionary changes in the construction materials industry.
Next up, a quick trip inside to look at the internal layout of the Colosseum, and how it effectively handled large crowds and groups of performers.
Globe Trotting Building Hugger 