🕑 Reading time: 1 minute
The Colosseum, Rome’s greatest amphitheater, was commissioned by the Emperor Vespasian in 72 CE. It is built on the marshy site of an artificial lake and provided the Romans a venue for hosting executions, animal hunts, gladiatorial games, re-enactments, and dramas. At the time of its construction, it was called the Flavian amphitheater. Later on, the amphitheater came to be known as the Colosseum after the colossal statue of Sun located near it.
The building is the largest of all Roman amphitheaters, with a regular elliptical plan measuring 188×156 m externally on its major axes. The foundations are a ring of concrete 13.5 m high and 54 m wide, set 9 m deep into the clay bed of the artificial lake.
The amphitheater is oval in shape and consists of four stories. The ground floor had 80 entrances, which were constructed in a ring shape. It was constructed on 2.4 ha of land. According to ancient texts, the structure had a seating capacity for 87,000 individuals.
Although two-thirds of the colosseum has been destroyed over time, mostly due to vandalism, earthquakes, and fires, but the building itself is appreciated as a triumph of planning and engineering and a symbol of the invincible Roman Empire.
1. Materials Used for Construction
The three primary materials used in the construction of the amphitheater were tuff, concrete, and travertine. Travertine is a type of limestone that was regarded as a very strong construction material by the Roman builders.
Tuff is a type of volcanic stone, which was used as a construction material due to its weight. Tuff is very soft and lighter compared to travertine. However, it has a good compressive strength.
Concrete, during the Roman period, consisted of small stones and mortar. Romans had created a new kind of mortar that consisted of fine-grained volcanic ash instead of sand. Lime and water were used as the bonding material for the mortar.
The builders also used bricks and iron clamps. Around 272 metric tons of iron clamps were used in the construction.
1.1 Grading of Materials
The designers of the Colosseum chose the ideal materials suitable for different parts of the structure. Even during that time, the builders understood that the lower blocks should be able to support the weight of the upper block. Therefore, they placed the heaviest stones in the lower parts of the structure and lighter stones in the upper part.
This was referred to as grading of material during the Roman era and such practices are used even today by the housebuilders.
2. Foundation Details of Colosseum
The construction of the Colosseum was a herculean task mostly to its huge weight. A strong foundation was needed to handle such an enormous weight. However, the greatest challenge was to construct the amphitheater at the site of a lake due to the scarcity of open land in the central part of Rome.
Firstly, builders drained all the water from the lake and then excavated a 6 m deep trench. The excavation was carried out by hands and therefore, it took around one year for the complete excavation of the site.
Further, they built two foundation walls in an oval shape with the outer wall of the foundation following the edge of the trench. Each wall was constructed with a height of 12 m and a width of 3 m. Concrete was used in the construction of the wall and bricks were used as facing material for the walls. Concrete was used as a filler between the inner and outer wall.
This giant donut of concrete was the perfect foundation to uniformly disperse the structure's weight. Further, the tunnels were constructed by dividing the foundation into four areas. One central tunnel was constructed along the length of the oval from one end to another, and three tunnels were constructed side by side to the main tunnel.
Drains were constructed under the tunnels and sloped outwards. The purpose of the drains system was to collect rainwater. Therefore, this would keep the arena dry during the rainy seasons as the structure was located in the lower part of the city.
The world's largest amphitheater still stands firm today because of a well-built foundation.
3. Construction Process of Colosseum
After the construction of the foundation, the construction of the superstructure was started. Vespasian wanted the construction to be completed at the earliest and therefore, the structure was divided into sections to increase the speed of construction. Though the basic plan was the same for all the sections, a slight difference developed in them which is still visible in the structure.
The flooring of the structure had to support the strong seating of stones, for which solid flooring was required. But the solid flooring would obstruct the flow of people from entering the amphitheater, therefore the construction of arches was considered to solve this problem.
3.1 Construction of Arches and Vaults
Arches can support more weight than beams because the shape of the arch distributes the weight to the supporting sides more evenly. Roman builders combined the arches and formed ceilings called vaults. Further, the builders covered the arches on one side along the columns to form the arcade. This provided access for entering into the amphitheater from all the sides.
Romans were the very first ones to use concrete for making arches. The concrete vaults in the Colosseum resulted in a durable structure that was very simple to enter and exit from.
4. Design of the Colosseum
The amphitheater was so well designed that the entire audience could empty the structure within minutes. The following points describe the design of the Colosseum:
- The fundamental design of the Colosseum is a series of ovals that used to lead people from the outdoor walls to the arena.
- Tunnels constructed for drainage purposes were used by the gladiators to enter the arena through the basement.
- Trapdoors around the arena's wood flooring enabled gladiators to appear in the arena as if they appeared by magic.
- Seating levels were provided in the form of stone chairs. Every level was constructed in such a way that the seating chairs of each level were connected to the arcades.
- The ground-level arcade consisted of around 80 entrances, out of which 76 entrances were used for the public.
- Arches and vaults were constructed in such a way that they would directly lead to the staircases and corridors on each level.
- Each level was divided into several seating sections with every arch section having its separate staircase.
5. The Colosseum Today
The Colosseum continued to host gladiator games and animal fights for centuries. However, as soon as the Roman Empire collapsed, the condition of the Colosseum deteriorated majorly due to the lack of funds for maintenance work.
Later on, an earthquake shook the structure and several columns and arches of the Colosseum collapsed. People of Rome used the structure for stabling animals, growing vegetables, and dumping trash. The travertine blocks were taken away by people for their personal uses. Finally, in the 16th century, the local governing body of Rome put an end to such activities.
Regardless of all the damage, the Colosseum still stands strong today. It is considered among the seven wonders of the world and as one of the prominent tourist destinations in Italy. The Italian government has planned to restore the entire structure and it has also proposed to host large cultural and sport events inside the Colosseum as it is still a very strong and structurally sound amphitheater.
The Colosseum had a height of 48 m. It was more than 189 m long and 156 m wide and covered a large area of 2.4 ha.
More than 900,000 metric tons of travertine, limestone, concrete, brick, and a type of volcanic stone were utilized in the construction of the Colosseum.
The Colosseum was the biggest Roman amphitheater ever built. It had a seating capacity of 87,000 or more individuals.
A Wall foundation was provided for the construction of the Colosseum. Two walls in an oval shape were constructed, having 12 m of height and 3 m of width.
Structural Details of Burj Khalifa – Concrete Grade and Foundation
Repairs and Rehabilitation of Concrete Structures for Failure and Defects