Engineered for Entertainment: a Design Comparison Between the Colosseum and the Theater of Ostia Antic

Written by: Anthony Brim

All photos and figures belong to author unless otherwise specified

Introduction

The Colosseum, constructed by emperor Vespasian starting in 72 AD and dedicated by his successor Titus in 80 AD, was the epicenter of Roman entertainment (Welch, 2007). Additionally, it remained the largest amphitheater ever constructed in the time of the Roman empire, covering an area of 188 x 156 meters (Welch, 2007). Upon visiting the Colosseum, spectators got to enjoy executions, showcases of exotic animals, and gladiatorial games. Today, it remains a popular tourist attraction in the center of modern day Rome, drawing visitors from all over the world.

Approximately 15 miles west of Rome along the Tiber river, exists the ruins of the ancient Roman city known as Ostia Antica (Boyce, 1945). This is the home of an older, less widely known Roman entertainment center. The theater of Ostia Antica is believed to have been constructed sometime during the 1st century BC (Gugliermetti, 2008). Having originated as a military settlement to control passage through the Tiber, the city began to thrive with the construction of a bridge across the river, connecting it to Rome (Gugliermetti, 2008). This connection brought economic and cultural growth that led to the theater’s construction (Gugliermetti, 2008). Unlike the Colosseum, the theater was not used for games, but instead hosted performances of drama.

Though the structures’ architecture and design are comparable due to the similar purposes they shared, there are several intentional differences in these designs that will be covered in this article.

General Anatomy

It is difficult to compare the Colosseum and the Ostia Antica theater without a basic understanding of each structure, so let us get familiar with them before we continue.

The design of the Ostia Antica theater, originating from ancient Greece, took on the shape of a half-circle and consisted of four main parts. The first part was the cavea, where the spectators were kept (Gugliermetti, 2008). In front of that was the orchestra, which was either reserved for people of importance, such as senators, or filled with water for naval scenes during the latter years of its operation (Gugliermetti, 2008). beyond the orchestra, was the skene, the space which belonged to the actors and included the proskenion (stage). Finally, behind the cavea existed the portico, which is essentially a columned passage, that acted as shade for the theater inhabitants and also helped with the acoustic design that will be discussed in a later section (Gugliermetti, 2008). Unfortunately, the portico and much of the skene no longer exists today.

The design of the Colosseum, known more generally as the amphitheater is thought to have originated in Italy and appears to be derivative of the Greek theater, with the half circle being extended to a full circle (Rindel, 2013). Like the theater, the Colosseum consisted of spectator sections for common folk and nobility, and even had a decorative porticus on the top floor sporting Greek-inspired pillars. Instead of a skene, there is an arena in the middle of the establishment. Unlike most other amphitheaters of the time, it was also possible to remove the center floor of the arena and fill it with water for mock sea battles (Welch, 2007).

Architecture and Design Choices

Given that both the Colosseum and the theater of Ostia Antica shared almost the same purpose, to put on a show, these structures are very comparable in how their architecture functioned to provide an exceptional experience for everyone who attended their events. However, there were dome key contextual differences that inspired different design choices in these structures. This section aims to explore those similarities and differences.

Built for the masses

Perhaps the most obvious difference between the Colosseum and the theater of Ostia Antica is the scale. Ancient Rome was not only home to the emperor but also hundred’s of thousands of Roman citizens. The Colosseum was meant to be enjoyed by people of all classes, from peasant to nobility, and therefor was required to accommodate vast amounts of spectators. According to the book ‘The Roman amphitheatre: from its origins to the Colosseum‘ written by Katherine E. Welch, the Colosseum was capable of supporting approximately 50,000 people (Welch, 2007). On the contrary, Ostia Antica was a much smaller city, so the designers of the city theater were not nearly as burdened with a large population in mind. The theater was said to have hosted an audience of a mere 3,000 spectators (Gugliermetti, 2008).

One challenge posed by the number of spectators was the increase in structural demand, not just for the extra people, but also for the seating structures to accommodate them. Both the Colosseum and the Ostia Antica theater consisted of multiple floors that needed to be well supported to ensure a safe and serviceable structure. In this case, the answer to this problem was the same for both structures, and that answer was arches.

Arches offer structural advantages that the Romans understood and made extensive use out of. An arch can transfer loads from above into columns below that save material and create access points while still maintaining sufficient strength to uphold a structure.

Figure 4 depicts a simple diagram demonstrating the mechanics of an arch structure. The value w represents the equivalent distributed load acted on the arch by the structure and spectators above. The vertical reaction forces, denoted as Ry, are each equivalent to half the total value of distributed load w assuming a normal load distribution. The horizontal reaction forces, denoted Rx, are resultant from the distributed load’s tendency to move the arch outward due to the moment the load creates relative to each end. Under the same assumptions as before, Rx is equivalent to the equation displayed with figure 4, where L is the total arch length and Yc is the arch’s maximum height.

The Colosseum made extensive use of arches. There are hundreds of arches both extending across the facade and throughout the inner structure of the stadium that once held three floors of spectator seating. Not only did these structures stand strong during the recreational activities of it’s time, but they have also kept much of the Colosseum standing after earthquakes and hundreds of years of neglect, albeit with some renovation.

The theater of Ostia Antica had a similar facade lined with multiple series of arches to hold up the three levels of the cavea as well as the porticus. Upon visiting the site, I noticed that what remained of the arches was limited to the facade and the area beneath the cavea appeared to be filled in, unlike the Colosseum, with its extensive array of arches and vault structures beneath the upper floors.

Another, more logistical challenge of having large numbers of spectators is moving them efficiently from the outside to the seating areas. The arches that made up the Colosseum allowed the creation of corridors that led to multiple entrances around the building for each floor. This system is most comparable to modern day stadiums such as the Stadio Olimpico, the Roman center for Olympic sports turned popular football venue, which now hosts two of Rome’s most popular football teams.

The structure of the theater of Ostia Antica is most comparable to modern day theaters, in which the audience is allowed to enter on one side of the venue while the actors used the other. The theater has a relatively simple, yet efficient arrangement of entrances. A passage through the center of the cavea and two other public entrances on either side of the theater served as entryways for the lower seating area (Gugliermetti 2008). two additional staircases on either side of the central entrance served as easy access for spectators headed for an upper level.

Testing, 1, 2, 3: Acoustic Design and Performance

One of the most impressive things about the Roman amphitheaters is their ability to carry sound without the use of modern sound systems. During a class tour of the Ostia Antica theater, I remember sitting in the lower part of the cavea while the class tour guide conducted an audio demonstration with a couple of my peers on stage. They spoke to us from the stage and we could hear them with complete clarity, and even whispers could be picked up with very little difficulty. But how did the Romans, and the Greeks before them, achieve this effect?

The answer to this question is provided in great detail by Vitruvius, a well known ancient Roman architect and engineer of the 1st century BC. According to Vitruvius, the overall concave structure of the theater helps to reflect sound and amplify it so all are able to hear it (Rindel, 2013). Additionally, surfaces towards the front, such as the floor of the orchestra, were covered in marble to further increase the reflected sound (Gugliermetti 2008). Evidence of both these techniques is still visible today.

According to Vitruvius, there was more to it. He mentions the use of sounding vessels made of bronze placed under the seats in specific positions and on specific levels (Rindel, 2013). Because Vitruvius explains the vessels are there to increase the clarity of the stage performers these vessels are thought by experts to have been designed for sound absorption rather than reflection (Rindel, 2013). These vessels have so far eluded experts, and much of the information we have on them comes from Vitruvius’ writings (Rindel, 2013). Also missing from what’s left of the theater were wooden panels positioned at an angle on top of the facade of the skene which turned the section into its own concave structure that was capable of reflecting and amplifying sound for the audience (Rindel, 2013).

The Colosseum was designed with different constraints in mind. Spectacles held at the Colosseum emphasized visual elements more than they did vocal elements, so there was less need for sophisticated sounding techniques in its construction and operation. However, that does not mean sound design was neglected entirely. The bowl shape of the Colosseum mimics the concave half circle of the theater and has many of the same audio effects. In addition, many surfaces of the Colosseum were decorated with marble, which would further help reflect soundwaves.

During my class visit to the Colosseum, I noticed that from every floor, I had a clear view of the center arena. This was because every floor of the structure was lofted relatively high above the previous one, ensuring everyone had a good view of the show going on in the center of the arena. Premium seating was located right at the edge of the arena just one level up to ensure important public figures and their relatives had the clearest view of the main event.

Material Usage

Having been built in the same area, both the Colosseum and the theater of Ostia Antica use many of the same materials. The main difference between the two structures is mostly cosmetic, as the Colosseum was much wealthier than the theater due to historical context that will be discussed below.

The Bones: Structurally Significant Material Compositions

Much of the material structure of the Colosseum has become known after years of archeological study. While it was a very rich looking structure at it’s peak, it’s actual strength came from something a lot less nice looking, though no less impressive in my opinion. The structurally significant portion of the Colosseum was made of three main materials: Travertine, tuff, bricks, and concrete.

A combination travertine blocks, a mineral formed around volcanic springs and also a popular choice in Roman construction, and tuff blocks, a mineral formed with the settling of volcanic ash, was used in both the facade of the building and the paving (Lancaster, 2005). Beyond that, the Romans constructed brick quadrants held together by mortar (Lancaster, 2005). Within the center of these quadrants, pozzolanic concrete was poured to fill them in and add more strength (Lancaster, 2005). most of the travertine and tuff blocks that made up the superstructure were connected to each other using iron dowels (Lancaster, 2005).

Unfortunately, less is known about the material composition of the theater of Ostia Antica. What is known is much of the city was constructed using tuff, bricks and concrete, much like the Colosseum, and that likely includes the theater.

Some visual inspection of the theater reveals that brick and mortar was certainly used in it’s construction (see figure 15 below). In addition, much of the seating area was made up of pozzolana concrete. As for the columns of the porticus, it is believed that they were made primarily out of tuff (DeLaine, 2018).

Displays of Wealth

While one side of architectural design is concerned with structural stability and functionality, the other side is concerned with making the place look nice. In the case of the Colosseum and the Ostia Antica theater, establishments concerned with the enjoyment and comfort of the visitors, the latter is especially true.

Marble was the popular decorative choice for ancient Romans at the time of both of these venues, and was used to cover large portions of the surfaces of both structures. However, the marble selection for the Colosseum differed widely from that of the Ostia Antica theater. This is due to the fact that Ostia Antica didn’t have remotely as much access to wealth as Rome, where large projects like the Colosseum were directly supported and enjoyed by emperors and senators (DeLaine, 2018). Marble used in Ostia Antica was likely limited to closer sources around Italy (DeLaine, 2018). On the contrary, the Colosseum displayed wealth through a variety of marbles originating from all over Europe and the Middle East.

Conclusion

So what is the point of learning about these structures other than to appease our curiosities about life in the past? Well, it turns out that structures such as the Colosseum and the Ostia Antica theater may have influenced some of our more modern buildings.

Earlier in the article, I likened the Colosseum to modern day sports stadiums like the Stadio Olimpico. Though the specific designs of sports stadiums utilize more modern engineering techniques and materials, such as structural steel, the main shape and general idea of the Colosseum and these stadiums is the same. In the case of the theater of Ostia Antica, not only can it be likened to modern theaters, but also university lecture halls, which use some of the same principles of sound reflection and non-electronic amplification. This just goes to show how understanding of things from even over 2,000 years ago can broaden our understanding of the modern world, and maybe even inspire improvements for future projects.

As I researched and visited these sites, I marveled at how much thought went into the design of each of these structures. Despite having limited knowledge of structural engineering and acoustic physics, the Romans were able to engineer extremely sophisticated entertainment venues for their time, exploiting techniques from both of these subjects in the most aesthetically pleasing ways possible. The ancient Roman use of form and function in their buildings is certainly something to draw inspiration from.

References

Parco Archeologico Di Ostia. (2017). Archeological Preview of Ostia Antica Theater. beniculturali. Retrieved September 16, 2024, from https://www.ostiaantica.beniculturali.it/en/educational-panels/the-area-of-the-theatre/the-area-of-the-theatre-and-the-headquarters-of-the-trading-corporations/.

Gugliermetti, F., Bisegna, F., & Monaco, A. (2008). Acoustical evolution of the roman theatre of ostia. Building Acoustics, 15(2), 153-167.

Lancaster, L. C. (2005). The process of building the Colosseum: the site, materials, and construction techniques. Journal of Roman Archaeology, 18, 57-82.

DeLaine, J., & Brysbaert, A. (2018). Economic choice in Roman construction: case studies from Ostia. Constructing Monuments, Perceiving Monumentality and the Economics of Building: Theoretical and Methodological Approaches to the Built Environment, Leiden, 243-69.

Boyce, A. A. (1942). Ancient Ostia. Scientific American, 166(2), 70-72.

Welch, K. E. (2007). The Roman amphitheatre: from its origins to the Colosseum. Cambridge University Press.

Rindel, J. H. (2013). Roman theatres and revival of their acoustics in the ERATO project. Acta acustica united with acustica, 99(1), 21-29.