The Colosseum, a Roman Empire amphitheater built in the first century, is located in the eastern part of the Roman Forum. It was the largest of all the amphitheaters built in the Roman Empire. Its original name was Flavian Amphitheater, but later it was called Colosseum due to the nearby presence of the Colossus of Nero, a statue in honor of Emperor Nero that underwent changes and eventually disappeared.

For its construction various materials were used such as travertine blocks, concrete, wood, brick, stone (tuff), marble and stucco. In its time, it had the capacity to hold approximately 65,000 spectators distributed in eighty rows of bleachers. The seats closest to the arena were reserved for the Emperor, his family and the senators, while as one moved up the tiers, one found the lower social strata. The Colosseum was the scene of gladiatorial fights and public spectacles.

Construction of the Colosseum began between 70 and 72 A.D. during the reign of Emperor Vespasian and was completed in 80 A.D. under his son, Emperor Titus, with later modifications made during the reign of Domitian. Its inauguration took place over 100 days, with the participation of the entire Roman people and numerous deaths of gladiators and wild beasts for public entertainment.

It is possibly the most impressive work of Roman architecture, noted for its use of various construction techniques. The pilasters and arches were built using travertine without the use of mortar. Similarly, tuff was used in the lower parts and in the basements, and many of these pieces were secured with metal staples. The vaults supporting the tiers were created by pouring cement directly onto wooden formwork, a novel technique that reduced the weight of the structure.

The location of the building over a lagoon required the excavation of up to 14 meters of unusable mud and the construction of a base of almost 13 meters composed of alternating courses of lime and stone mortar, known as opus cementicium.

Over nearly five centuries, the Colosseum was used for a variety of events, including gladiator fights, naumachias, animal hunts, executions, reenactments of famous battles and theatrical performances based on classical mythology. In the High Middle Ages, it ceased to be used for these purposes and came to have different uses, such as shelter, factory, religious headquarters, fortress and quarry. Finally, it became a Christian sanctuary in honor of the Christian martyrs of early Christianity, which helped preserve its structure.

Despite the damage caused by earthquakes and the extraction of building materials over the years, the Colosseum remains an iconic symbol of Imperial Rome and one of the finest surviving examples of Roman architecture. It is one of Rome's main tourist attractions today and has a strong association with the Catholic Church, as the pope leads the Stations of the Cross to the amphitheater every Good Friday.

In 1980, the Colosseum, along with the historic center of Rome, was designated a UNESCO World Heritage Site, and in 2007, it was recognized as one of the seven new wonders of the modern world.