Engineering the Roman Colosseum While the Colosseum stands, Rome shall stand; when the Colosseum falls, Rome shall fall; when Rome falls, the world shall fall. -- The Venerable Bede quoting an Ancient Anglo-Saxon Peasant Prophecy

Perhaps the most enduring symbol of the greatness of the Roman Empire can be seen today in the ruins of the Colosseum. This massive amphitheatre is situated in the middle of modern Rome near the Roman Forum and has become an iconic representation of the Roman Empire at its zenith. Although estimates vary, analysts believe that at least 50,000 and perhaps as many as 80,000 spectators were accommodated in its capacious dimensions and the Colosseum has become the benchmark by which all subsequent stadia have been judged. Flush with the treasures and riches of Jerusalem, the builders of the Colosseum spared no expense in its design and construction, but despite its impressive seating capacity and functional design, opinions concerning the aesthetics of the Colosseum have varied over the centuries, with some scholars describing the structure in strictly superlative terms while others have argued that it lacks the aesthetic qualities that characterize other Roman architecture. To determine the facts, this paper reviews the relevant literature to provide the dimensions of the Colosseum, important architectural details and varying views concerning the end result. Finally, a summary of the research and important findings concerning the engineering of the Colosseum are provided in the conclusion.

Review and Analysis

Overview of the Colosseum

The location selected for the construction of the Colosseum was a level region situated between the Esquiline Caelian, and Palatine Hills.[footnoteRef:2] According to one historian, "Constructed in the city center, the Colosseum differed vastly from other amphitheatres that were typically located on the outer edge of a city. It emblematically stood, and still stands, at the core of Rome."[footnoteRef:3] Irrespective of any aesthetic considerations, the dimensions of the Colosseum are truly impressive even by modern standards and its general dimensions are provided at Appendix A. IN sum, the dimensions of the Colosseum were 189 meters (615 feet) long and 156 meters (510 feet) wide; the structure's base area covers six acres and the height of the outer wall is 48 meters (157 feet), making it as tall as a modern 12-15 story structure.[footnoteRef:4] [2: Gulomar Barbi, "The Colosseum," The World and I, 22(9) (2007, September), 37.] [3: Barbi, "The Colosseum," 37.] [4: Barbi, "The Colosseum," 37.]

Although significantly smaller today due to the harvesting of stones for local construction projects, the Colosseum's perimeter was originally 545 meters (1,788 feet) and the central arena's oval was 287 feet long by 180 feet wide, and this enclosure was surrounded by a 15-foot high wall.[footnoteRef:5] A number of different types of locally sourced building materials were used to construct the Colosseum, including a type of limestone ("travetino") stones, tuff (which was used for radial walls and some pillars), ceramic tiles (also used on the walls and for the flooring of the upper levels), and concrete which was used for the vaults.[footnoteRef:6] Although the historical record is unclear on the issue, it would appear reasonable to suggest that the floor of the main arena of the Colosseum was also made from some type of water-proof concrete. For instance, Grayson notes that, "The Romans restaged battles in the Colosseum so that the vulgar could celebrate famous victories in which the players were actually killed and, if it was a naval engagement, the arena was filled with water."[footnoteRef:7] [5: Barbi, "The Colosseum," 37.] [6: "Colosseum building materials," The Colosseum [online] available: http://www.the-colosseum.net/architecture / materials_en.htm, 3.] [7: Richard Grayson, "History Will Repeat Itself: Strategies of Re-Enactment in Contemporary (Media) Art and Performance," Art Monthly 313 (February 2008), 27]

In fact, there were two different types of mortar used in the construction of the Colosseum, with one type (pozzolanic mortar) being waterproof which could account for the ability of Roman engineers to flood the arena for naval battles without flooding the structure's lower levels. This type of mortar consisted of "pozzolana," made from volcanic ashes that had been sufficiently heated to produce its Portland concrete-type water-proof qualities.[footnoteRef:8] In his study, "The Riddle of Ancient Roman Concrete," Moore reports that Roman engineers discovered by trial-and-error that when a small amount of volcanic ash was reduced to a fine powder and mixed with moist lime, it produced a water-proof concrete that would even cure underwater.[footnoteRef:9] An important finding by Moore was that the Roman engineers also used special construction methods with this type of concrete. In this regard, Moore advises that, "We have learned that ancient concrete was a simple mixture of wet lime and pozzolan in specific ratios to match the desires of the Roman architect. We have also learned that the Romans...

[online] available: http://www.romanconcrete.com/docs/spillway/spillway.htm, 2.] [10: David Moore, "The Riddle of Ancient Roman Concrete," 4.] [11: David Moore, "The Riddle of Ancient Roman Concrete," 4.]
The various building materials used in the construction of the upper levels of Colosseum were undoubtedly moved into place using a human-powered treadmill crane of the type depicted in Figure 1 below. In this regard, one historian reports that, "Columns and other massive blocks were raised by means of a crane with its system of pulleys. Motive power was supplied by men in a treadmill -- a huge wooden wheel."[footnoteRef:12] [12: Frank Gardner Moore, The Roman's World (New York: Biblo and Tannen, 1971), 349.]

Figure 1. Typical human-powered treadmill crane used in the construction of the Colosseum

Source: http://www.the-colosseum.net/images/macchine.jpg

All attendees at the Colosseum's events received tickets (made from pottery shards) with a number and the amphitheatre contained 80 separate general public entrances/exits marked with corresponding Roman numerals (as shown in Figure 2 below) that facilitated rapid seating and egress.[footnoteRef:13] According to one historian, "The entering and exiting of the Colosseum was methodically planned. There were eighty entrances at ground level. Both entrances and exits were numbered, as was each staircase. Four specific entrances were roped off for VIP guests."[footnoteRef:14] The reigning Roman emperor and the Vestal Virgins had the northern main entrance reserved for them and the other three entrances/exits were likewise reserved for the Roman elite[footnoteRef:15] As shown in Figure 2 below, the highly coveted entrances and exists that were reserved for the Roman elite were marked by their names or red numbers (as discussed further below).[footnoteRef:16] [13: Barbi, "The Colosseum," 37.] [14: Barbi, "The Colosseum," 38.] [15: Barbi, "The Colosseum," 38.] [16: Barbi, "The Colosseum," 38.]

Figure 2. Entrance/exit to the Colosseum marked by Roman numeral

Source: http://www.italoamericano.org/

In 2013, a $285 million renovation project began on the Colosseum that has since revealed some other interesting facts about the amphitheater's entrances and exits, some of which have been discovered to have been painted in red numbers. According to staff writers at L'Italo-Americano, "[Red] numbers were painted on the arches to indicate the different sections of the amphitheater, very similar to a modern stadium. Experts found out that the maximum visibility was obtained through the rubricatura technique, named after the ruben red color or by coloring the groove of each number."[footnoteRef:17] This coloration method served to ensure maximum visibility of the red-numbered entrances/exits and just four such portals, all placed on the structure's minor axes, have been discovered. The small number of such specially reserved entrances and exits was likely due to the high political and social levels of the patrons that used them.[footnoteRef:18] [17: "The Colosseum renovation unveils a series of numbers in red paint," L'Italo-Americano [online] available: http://www.italoamericano.org/social/colosseum-renovation-unveils-series-numbers-red-paint, 3.] [18: "The Colosseum renovation unveils," 4.]

Although estimates vary, modern researchers place the seating capacity of the Colosseum at about 50,000 spectators, but these spectators were carefully segregated according to social status. In this regard, Barbi reports that, "As was the case with the distinctive entrances, special boxes were provided at the north and south ends respectively for the Emperor and the Vestal Virgins. Naturally, those seats had the best views of the arena.[footnoteRef:19] The seats between the emperor and the Vestal Virgins were reserved for Roman senators and some names of these attendees carved into the masonry can still be discerned as shown in Figure 3 below. [19: Barbi, "The Colosseum," 38.]

Figure 3. Roman senator's name carved into masonry at the Colosseum

Source: http://www.acoupleontheroad.com/wp-content/uploads/2014/02/untitled-7-of-14.jpg

Beneath the central area's ground level, the Roman engineers built a series of large rooms for human activities such as preparations for the events that would be held in the arena above as well as wild animal cages and various mechanical devices such as massive elevators to make gladiators, wild animals and scenery appear as if by deux ex machina-type magic in the middle of the central arena.[footnoteRef:20] In this regard, one historian reports that, "The arena floor was made of wooden planks supported by…