Engineering Rome


Amphitheatrum Flavium
The Structure and History of the Colosseumsarjer sarjer Sep 16, 2013


When thinking about Rome, the Colosseum is often the picture that most people get. This makes sense, as it is an iconic image of the city, recognized throughout the world. It is Rome’s most popular tourist attraction, bringing in almost six million visitors each year (Pepe). As I have known about the Colosseum for years, I never had the opportunity to visit until a recent three-week civil engineering program to Rome through my university. My initial thoughts were that it would be a large, old building that would be interesting to see and take some touristy pictures with. After some engineering [[#|classes]], site visits, and detailed tours, I have found the Colosseum to be a [[#|complete]] masterpiece with fascinating historical information and engineering ingenuity. Seeing this structure in person made me want to find even more information about its history, engineering and architectural ideas, and renovations. However, even after all the research, someone would have to see the Colosseum in person to appreciate the two thousand year old building and why it is one of the world’s most popular landmarks.


Dating back to the first century, the Amphitheatrum Flavium is one of the oldest buildings still around. It got its name from the three emperors who ruled during the building of the Colosseum or Flavian dynasty (Figure 1). The land, which the Colosseum now sits on, was once a man-made lake, called the Domus Aurea, created by the emperor Nero (Figure 2). The water was supplied from the Aqua Claudia aqueduct (Colosseum). During his reign, Nero also had a massive 30-meter statue of himself erected, the Colossus Neronis. It was originally built right beside the nearby Palatine Hill (Colossus of Nero). After the Great Fire that ran through in 64 A.D., destroying all the buildings through the valley, Rome was left with nothing. When Nero died shortly after, Vespasian took over as emperor and initialized plans for the Colosseum. The Domus Aurea was filled in, leaving a clay settlement for the foundation and the Colossus Neronis was moved outside the Colosseum. It no longer represented Nero, but was changed to the Roman Sun God. Eventually, the statue fell over, either from earthquakes or war, but the date is unknown. Today, many believe that is how the Amphitheatrum Flavium got its nickname (Colosseum).

Figure 1: The three ruling emperors of the Flavian Dynasty (ALRI)

Figure 2: Map of Italy (Colosseum)

Construction for the Colosseum began in 73 A.D. and had the first inaugural games in 81 A.D. Before the Colosseum, there were other arenas under the rule of Nero, but after the fire that destroyed most of Rome, the structures were ruined. When Vespasian took over after Nero, he wanted to build the Colosseum for the public’s approval during a hard time. After the Jewish war, the Roman’s had the means for completing the project. Thousands of prisoners were taken as slaves to build the structure and wealth was taken from Jerusalem for funding. Stones were found 20 miles away in Tivoli and carried back by the slaves to the site. The majority of construction had been completed when Vespasian passed and the final project was finished under his heir, Titus in 80 A.D. (Alchin).

Changes to the Colosseum were almost immediate. There were renovations by Titus’ son Domitian, who added the underground tunnels, known as the hypogeum, and extended the levels for more seating (Alchin). Additional constructional changes were added later because of fires and earthquakes. The Colosseum was basically rebuilt after a major fire during the 3rd century, with repairs lasting decades. There was also the massive earthquake, which caused severe destruction including the collapse of part of the exterior wall. During years of abandonment, people started to take the materials from the Colosseum, leaving damage still noticeable to day (Pepe).

The Colosseum was originally built for games between gladiators and animals. However, the uses changed over the years. When the fighting games ended in the 5th century, the Colosseum was abandoned and reclaimed as a cemetery. Around the 7th century, the Colosseum was owned by the Santa Maria nova, which rented out the arena as houses or shops. There after, Christians used it religiously because it was believed to be a sacred place for martyrs. Pope Benedict XIV added crosses around the Colosseum and lived there for the later part of his life, protecting the materials and initializing a restoration. Around the start of the 19th century, people began to recognize the archaeological significance of the site and huge restorations were set in place. As work began, large discoveries were found underground and historical material was collected. This ancient masterpiece in Rome eventually gained National attention as the iconic centerpiece (Pepe).

Uses: The Gladiator Games
The Colosseum served as an entertainment piece of infrastructure for the Roman’s, as the home of fighting between people and animals. The stadium could hold 50,000 spectators of all social classes. There were four levels of seating, which showed off the Roman social hierarchy (Figure 3). The north and south ends had special boxes with the best views, so they seated the emperor and Vestil Virgins. The senators had the next best seats, taking up the remaining first level. Their seats were stones with their names engraved on them and some have been recovered from the original first level seating. On the second tier, called the maenianum primum, the noble class had seats made of stone and marble. The third level was called the maenianum secondum, which seated standard Roman citizens. There were two parts to this section, the lower part for the wealthier and the upper for the poorer. Under Domitian, another level of seating was made for slaves and women to enjoy the games. These seats were either wooden benches or else standing sections. Similar to stadiums today, all the levels, sections, rows and seats were labeled with numbers and even names on the bottom tiers (Colosseum). Spectators were given stone tablets as “tickets” for their seat.

FIgure 3: The seating hierarchy of the arena (Pepe)

Animal fighting was very common and lasted longer than the human duels. In just the inaugural games, over 9,000 animals were slaughtered. Eventually there were so many deaths, species taken from Africa started to become endangered. The Colosseum was able to hold large animals so there existed fights between giraffes, elephants, and buffalos, to name a few. The games brought in an animal trading business to Rome. Slaves were in charge of maintaining the animals before their fights in the hypogeum (Alchin).

Humans who fought were called Gladiators, coming from their weapon “Gladius” or sword (Figure 4). They were introduced to Rome from Egypt in 260 B.C. (The Roman Gladiator). There have been 15 different classes of gladiators recognized (Pepe). Most often they were slaves, prisoners, or criminals who trained under a wealthy owner who had absolute rights. Condemned men, who did not fight under an owner, were sent to fight with no armor and left for death. If the owned fighters lost, the fate of their lives was left up to the decision of the emperor. All the winnings went to the owners. Otherwise, a gladiator could usually be freed after three years of fighting. There were also voluntary gladiators who were generally social outcasts, having committed a crime or a freed slave, but they needed wealth to fund their training and uniform. Occasionally, women were even known to have fought, but many considered these fights unethical. Their fights were called Munera (The Roman Gladiator). Gladiators who fought at the Colosseum trained at one of the four nearby schools. These facilities had tools for strength, rooms, and mini arenas for the gladiators to practice. The biggest school, Ludus Magnus, even had an underground passage attaching it to the hypogeum of the Colosseum (Alchin).

Figure 4: Gladius, weaponry used by the gladiators (Gladius)

Some of the games combined animal and human fighting. Games where humans hunted animals, generally with a spear, were called venationes. Venatores also trained in the same schools as gladiators for their hunting fights. Gladiators who fought the animals were called Bestiarii and they also trained in schools for their fights with their own uniform and weapons. Thousands of animals died from these fights. There were also mock games to depict a historical triumph for the Romans. Sometimes water was even used to mimic a naval scene (Alchin).

Gladiator games became part of the Roman culture both politically and socially, as a cheap form of entertainment and for self-promotion. When the inaugural games were introduced, they lasted for 100 days. However, they usually happened for about ten days in a row, twice a year (Alchin). Gladiator games were most popular during the Imperial Cult, between 108 and 109 A.D., where there were 10,000 gladiator fights and 11,000 animal fights (Pepe). The schedule and organization was even listed under Roman law. Eventually the intensity died down, as there began to be challenges against Christian morality with the killings and an abolishment of paganism. At this time, theater and chariot races were also gaining popularity from the public. Gladiator fights have been recorded through the beginning of 5th century and animal killings until the 6th century in the Colosseum (Alchin). The Colosseum also had public executions during these times, including a mass execution of non-Christians (Pepe).

Engineering Significance
The Colosseum is one of the great examples of Ancient Roman architecture and engineering exhibiting many of their achievements. The Colosseum was the beginning of many engineering advancements for the Romans, not only in materials like concrete, but also in structures (Pepe). Cross vaults, which were recently introduced, were used throughout the third level of the Colosseum. There were also three different types of ribbing throughout the original Colosseum and another new kind introduced during the renovations of the 3rd century. Between the original 1st century building and 3rd century construction, the Romans changed their philosophy on weight dispersion. It was initially to have their structures with individual pieces able to withstand greater loads. Eventually the Romans switched their ideas to having their large weights dispersed over greater areas (Lancaster). Over the years, the engineering flaws have also become apparent. Nonetheless, the Colosseum is still an impressive engineering contribution to Rome.

Since the Colosseum was being built over a dried lake, the Romans had to make sure it was completely drained before laying foundation over the remaining clay bed. The foundation went down for 12 meters and was 530 meters in diameter. Roman concrete was the source for the foundation, covering the ground and providing chambers to build walls off of. There were four tunnels made by covering the wooden foundations with concrete, with four drains underneath. The finished Colosseum is 188 meters long, 156 meters wide, and 48.5 meters tall (Pepe).

The Colosseum was a masterpiece that shows off the Roman’s superior and early understanding of materials. It was built just after the invention of cement so concrete and stone mainly assembled it. Cement was formed with limestone, which was heated and chemically formed into a paste. The cement formed from the limestone and sand was then hardened into concrete and used to help bind the stones. They were laid in regular horizontal rows (Pepe). The engineers were sure to use the heavier cements for the foundations and the lighter cement for the arches that structured the Colosseum’s four levels. This would provide a stronger base for lighter loads and stress (Lancaster).

Lightweight stones for the vaulted arches were made from yellow tuff (Figure 5), which was a volcanic product found near Rome and used as a binding element within the cement. This allowed for strong support without adding additional weight. Mortar, made with pumice stones, was cleverly used on the highest levels because of its lightweight (Lancaster). This demonstrates the great attention to detail by the Romans to their materials, specifically mortar. The travertine stones were found nearly 20 miles away in Tivoli and carried by the slave builders back to the site. Travertine stones were a limestone sedimentary rock (Figure 6) and helped build the main walls and floors. Since the Colosseum was made up of two parts, the interior and exterior, there were different materials for each one. The travertine stones were mainly used for the exterior wall and cavea, while the interior wall was made with tuff stones. The outer structure used the same travertine stone but instead of concrete, had metal sheets to connect the stones. There was 300 tons of iron used for these clamps, which since, most has been stolen. The Roman’s also decorated the Colosseum with tiles and bricks (made similarly) for wall structures or fillings. The arena part was comprised of wood with sand over it. Marble decorated the inside of the stadium and was used for the seating. Under in the hypogeum, there was lead and terra cotta used for the water and sewer systems. Combining different materials together helped to strengthen the building and reduce stresses (Pepe). Being able to understand the different materials weights and strengths allowed the Roman’s to be so successful in their projects.

Figure 5: Tuff (Tuff)
Figure 6: Travertine (Sungloss)

The Roman’s had so much early success in engineering due majorly to their understanding and perfection of the arches. There were 80 arches on each of the first three stories, which were numbered as entrances. The arches were made from concrete and were the main supporting point of the stadium. Arches work by carrying the forces from the weight they support to the ground. They create compressive stress on the inside bend of the arch, but relieve tension stress on the outside of the arch. On the first floor, the arches are 4.20 by 7.05 meters (Figure 7) and on the other floors they are 6.45 meters high (Pepe). The reason for the different heights is because as arches heights increase, the amount of thrust decreases. The arches around the Colosseum appear to be rounded and three pinned. The three pinned arches use hinges at the bases and in the middle, highest point. This makes the arch statically determinate, which can be seen in the arch analysis. Since the Colosseum was made with unreinforced concrete, the arches were able to move so three pinned arches were necessary for creating stability (Thompson).

Figure 7: Arches from the ground floor (Pepe)

Since the arches of the Colosseum were three pinned (Figure 8), I was able to complete an arch analysis. It is okay to apply this to the Colosseum because of the unreinforced concrete. The three pinned assumption works at the base hinges because settlement of the structure occurred. For the top pin, it is created because concrete is weak in tension and as gravity loads down on the arch, more tension will be created at the pin. In my analysis, I was able to solve for the reactions at the base points using equilibrium equations for the sum of moments around a point and the sum of forces around an orthogonal object (Thompson).

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Figure 8: Three pinned arch (Thompson)

Vaults: While cross vaults were used on the third level of the Colosseum, the first and second tiers used barrel vaults (Pepe). Barrel vaults were basically an extrusion of arches, that ran through the corridors (Figure 9). They utilize the same engineering technique as arches, dispersing weight toward the more stable walls. Cross vaults are the intersection of barrel vaults. Cross vaults provided more support because the thrusts went down on the supporting columns rather than the walls. When built in a continuous series, one barrel vault creates a major axis with subsequent barrel vaults running up to it (Vault).

Figure 9: The various vaults used in the Colosseum (Architecture)

Flooding/Water Management: At one point, an aqueduct flooded into the Colosseum, but there was a drainage system. There were even mock water battles for the first hundred years, so a man made lake was created. Eventually, this ended and masonry walls were added so flooding was impossible (Mueller).

Hypogeum: Under the arena, the hypogeum (Figure 10) was constructed under Domitian. This was a two story series of tunnels, which is what remains still intact in for visitors in the Colosseum. The animals and gladiators were kept here before their fights. There were 80 lifts to raise the animals in cages to the surface, where the animalscould enter the arena directly through trapdoors. For larger animals, there were hinged platforms, called hegmata. This can be seen from the tracks left in walls for guiding the cages (Colosseum). Workers would turn capstens, which were large semi-circles that acted as elevators, lifting the cages. The Roman’s utilized several pulley tools for these features. These tunnels also continued outside of the stadium to the training school of Ludus Magnus and for a special entrance for the emperor. After the end of the fighting games, the hypogeum had several other uses like gardens and storage. Mussolini eventually uncovered this underground region. The hypogeum still had not been thoroughly studied until the past couple decades. Today, the hypogeum still looks like ruins of old tunnels about a story high, overgrown with weeds (Mueller).

Figure 10: The wooden deck layered in sand, overlooking the hypogeum (The Colosseum)

Masts: Along the top part, or cornice, of the Colosseum were wooden masts to hold a screening for protection from the hot sun, known as the velarium (Figure 11). The screen was attached with rope and held at an angle to block the sun and cool down the fighters. Sailors worked the masts (The Colosseum).

FIgure 11: Showing how the velarium was once attached to the top of the Colosseum (Pepe)

Cavea: The cavea was the seating area of the Colosseum. There were the four levels of seating, with the bottom nicer seats made of stone or marble and the top level using wood. The cavea was made almost entirely of travertine otherwise. Barrel vaults used under staircases supported the seating area (Figure 12). Stairs separated the sections vertically (Pepe).

08 Colosseum Seating.jpg
Figure 12: Seating that has been renovated to show what it looked like during the games. Held up by barrel vaults (Europe).

Columns: Every floor of the Colosseum uses a different form of columns (Figure 13). The first three floors have Doric, Ionic, Corinthian style columns, respectively. The fourth floor has pilasters (Raunekk). Pilasters are columns that protrude from walls. They are used more decoratively, and cannot support the same weight of a traditional column (Pilaster). Doric columns were the first kind created, coming straight from the ground to support the weight of a horizontal beam. Grooved wedges surround them. Next came ionic columns, which are distinguished by the decorative spirals at the top. They also use a kind of platform, providing a thicker base. Corinthian columns are the most decorative on the capitals, or tops of columns. Ionic and Corinthian both have narrower shafts and have hollowing out, or fluting, through the center. All the columns help to relieve stress and send weight to the ground (Greek Columns).

Figure 13: The three different kinds of columns: Doric, Ionic, Corinthian (Architecture)

Ribbing: Three different types of vaulting ribs were initially used throughout the Roman Colosseum, all with varying purposes. After the 3rd century renovations, another type of ribbing was installed as well. Some of these ribbings were the first of their kind used by the Romans, paving the way for engineering ideas in other buildings. Vaulting ribs are the intersection of two to three barrel vaults. Barrel vaults are basically a series of extruded arches through a corridor. One of the three types was the arch made of travertine voussoirs, which were located in the arena substructures. Voussoirs are the individual travertine stones that create the semi-circle of the arch. They were set into the ends of brick walls, with relieving arches built into them. They were intended to transfer loads along predefined routes throughout the structure. Another type of ribbing used was the arch of radially laid Roman bricks, acting as the wedge shaped elements of the arch. These are used on the second level through both the inner and outer corridors. They were also used under staircases. The final type of original ribbing was the arch of radially laid bricks separated at the two edges by partial bricks. These served as transitions between different heighted vaults or to support a landing. The final ribbing built in the 3rd century was the beginning of lattice ribbing. It was used for the arches in doors and windows as well as for creating a stopping place while working with vaults. This was the ribbing that helped disperse the weight around rather than be strong enough to just accumulate it (Lancaster).

Almost immediately, Domitian made additions to the Colosseum, including the complicated tunnels underground known as the hypogeum. This was used for preparing the animals before fights, which could then be lifted through trap doors. After only a hundred more years, the Colosseum went under construction for repairs. There was a large fire in 217, caused by lightning, resulting in extensive damage as the Colosseum burned for days. Repairs were done using only the original framework. It took nearly 50 years for all the repairs to be complete (Pepe). This was when the Roman’s added a new type of ribbing for support, providing better dispersion of weight (Lancaster). Other renovations have been started from Rome being attacked. There was a Visigoth and Vandals sacking, causing damage. After the games ended around the 6th century, the Colosseum was basically left abandoned for years (Pepe).

Rome is also susceptible to large earthquakes, which have caused damage throughout the years. In the first thousand years, there were several large earthquakes causing bricks to fall. The great earthquake of 1349 caused the collapse of the southern exterior wall (Figure 14). The reason the whole structure did not collapse is because of the uneven soil left in the lakebed. The southwest portion was less stable. In 1703, another earthquake collapsed some arches on the second level. When Pope Benedict XIV moved into the Colosseum, he had the church restored and the collapsed arches rebuilt. He also protected the Colosseum materials from being stolen (Pepe).

Figure 14: From this angle, the collapse of the south wall is very apparent (The Roman Colosseum)

Since the Colosseum was always going between times of abandonment and usage, there were many little remodels done. The Santa Maria nova built a church inside the Colosseum and rented out little shops and stands to people. There was even a cemetery built in the arena at one point. Throughout time, people started taking materials from the Colosseum for other buildings, including the stone and metal ties connecting the stones. There are visible holes in the Colosseum today from where this occurred. Some of the stones taken have been seen used in other buildings around Rome. The third level cross vaults were remodeled in the 18th century, when people finally began to recognize the importance of the Colosseum. The cavea was remodeled in the 1930s but it was not very successful as it is almost entirely gone (Pepe).

Modern Impact
Today the Colosseum is used as a major tourist attraction, attracting more visitors than anywhere else in Rome. It was the center for fascist parades under Mussolini. Ever since the Hollywood film, Gladiator, the Colosseum has gone from one million tourists a year to six million tourists. The recent 25 million Euro project to renovate the Colosseum is occurring to save one of Rome’s oldest structures. In 2007, it was listed under the Seven Wonders of the World and has been on and off the list . It is the world’s largest amphitheater (Colosseum). It is impressive enough that such an old structure still has such modern impact.

Future Installments
While visiting, we saw that there were renovations happening to the outer part of the Colosseum. Apparently, the Colosseum is to be covered in scaffolds for the next three years undergoing a 25 million euro renovation. Diego Della Valle is funding the current renovation. They plan to do a much-needed rebuild of the entrances and façade. The monument is in need of stones as they have been regularly falling. The south side of the Colosseum also needs work done as it has been sinking in (McKenna). There has been damage due to vibrations and pollution. The Colosseum should return from its yellowish, grey color to the original white hue after the cleaning and crack repair (Figure 15). There is also a plan to renovate the hypogeum, possibly disrupting tourism. After the renovations, visitors will be able to see 25% more of the Colosseum than what was currently available. In exchange for the funding, Della Valle has access to the Colosseum logo and can advertise his company to tourists. Hopefully these renovations will extend the longevity of the Colosseum for future generations (Italy’s Colosseum).

Figure 15: The yellow, grey color to the stones caused from pollution (Colosseo)

My Visit
It is one thing to learn about a famous historical site but another thing to get to experience it. On my visit, our group got a private tour, which enabled us to go to “off-limits” areas under the supervision of our tour guide. We started by walking to the main area level, which was a wooden deck covered in sand. It was renovated within the last decade to mock the original area, which was also wooden and full of sand (Figure 16). Our tour guide explained they used sand as a quicker way to clean up after the fights because they could easily just sweep the bloody sand around for a new surface. Looking up, we got a view of what was left of the stands. We learned there were four levels or sections for the spectators to watch. The higher the social class, the better the seats so women sat on the highest level. Seats had the spectator’s names engraved on the stone and some of the original one’s were left on display in the museum. Currently, the stadium has some renovated seats as samples of what they looked like on the first level for tourists to see. They guessed the emperor sat closest to the Palatine hill, although this information has never been proven. From this same platform, we could see the ruins below where gladiators or animals were kept before a fight. Slaves were in charge of lifting the animals up in cages by an “elevator system”. There were trap doors in the wooden deck to lift the animals through. The stadium has two main arches across from each other. Apparently the winning gladiator would leave through the winner’s exit, while the loser (if alive still) awaited their fate, either exiting the loser’s tunnel or dying. The choice was left up to the emperor.

Figure 16: On my tour at the wooden deck, overlooking the hypogeum

Afterwards, we went underneath, although we could only stay in a small section. Some of the original tiling and stone was still there and many of the stones still stacked had been damaged. Over the years, people started stealing supplies like the metal holding the stones together so, the damage was visible. We also learned that the stones used to be white, but years of pollution have made them a dark grey color. At one time, there was even a church built under the Colosseum and although the original one was no longer there, a new one had taken its place. There are still services there today for people.

After this we went to the various levels of the Colosseum, which included the second deck and then up to the third, which was special for our tour. From here, we were standing right next to the perfectly angled split, where half of the Colosseum broke apart during an earthquake because of the different soils. There was a perfect view of the Arc di Constantine and Roman Forum. There were other viewing decks, but we were not able to go any higher because they were there for further renovations. We could see construction happening currently along the outer wall of the Colosseum that faced toward the Capital.

It was disappointing to learn that so much of the Colosseum had been renovated already, which I did not know prior to this visit. However, most of the renovations are still old, having been done in the 18th century. Coming from the Pacific Northwest, which is relatively new, it is unusual to see something so old. It is one thing to hear about the Colosseum and see pictures, but another to get to walk through something two thousand years old and actually see the original details. Getting a tour left me with information and images I could not get from the Internet. For example, I have found very little information about the church still built under the Colosseum. It was also helpful to grasp the way the Colosseum looked when it was built because our tour guide could point out the exact current location and then show a picture of how it looked years ago. It helped to make the connection easier. While anyone can look up information online, a tour of the Colosseum is necessary for appreciating it.

After my long trip to Rome with several historical visits and tours, I have still found the Colosseum to be the most spectacular. Today, we find entertainment in sports and movies, but back then people enjoyed watching others fight for their lives. Over the course of nearly two thousand years, the Colosseum has gone through many changes in both appearance and usage. While we are continually making engineering advancements today with the help of modern technology, it is hard to believe that the Roman’s were able to build such structures without the knowledge and tools we have. Yet the old buildings still standing today seem to have so much more detail and beauty. By taking this study abroad program and visiting the various Roman architecture sites, I have gained more of an appreciation for engineering and structural design. After my visit, I understand why it is one of the world’s most well known places and Rome’s top tourist attraction. It truly takes a visit to understand how impressive the Colosseum really is.

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