Italy

The Colosseum is an oval amphitheater in the center of the city of Rome, Italy, just nearby east of the Roman Forum. It is the largest ancient amphitheater ever built, and is still, despite its age, the largest standing amphitheater in the world today. Construction began under the emperor Vespasian (69–79 AD) in year 72 and was completed in year 80 under his successor and heir, Titus (79–81 AD).

The site chosen was a flat area on the floor of a low valley between the Caelian, Esquiline, and Palatine Hills, through which a canalized stream ran as well as an artificial lake/marsh. By the 2nd century BC, the area was densely inhabited. It was devastated by the Great Fire of Rome in 64 AD, following which Nero seized much of the area to add to his personal domain. He built the grandiose Domus Aurea on the site, in front of which he created an artificial lake surrounded by pavilions, gardens, and porticoes. The existing Aqua Claudia aqueduct was extended to supply water to the area and the gigantic bronze Colossus of Nero was set up nearby at the entrance to the Domus Aurea.
Further modifications were made during the reign of Domitian (81–96 AD). The three emperors that were patrons of the work are known as the Flavian dynasty, and the amphitheater was named the Flavian Amphitheatre (Amphitheatrum Flavium).

The Colosseu is built of travertine limestone, tuff, and brick-faced concrete. The Colosseum could hold an estimated 50,000 to 80,000 spectators at various points in its history and have an average audience of some 65,000.
The building was used for gladiatorial contests and public spectacles including animal hunts, executions, re-enactments of famous battles, and dramas based on Roman mythology, and briefly mock sea battles. The building ceased to be used for entertainment in the early medieval era. It was later reused for such purposes as housing, workshops, quarters for a religious order, a fortress, a quarry, and a Christian shrine.

After Nero's suicide and the civil wars of the Year of the Four Emperors, the Colossus of Nero was remodeled by the condemned emperor's successors into the likeness of Helios (Sol) or Apollo, the sun god, by adding the appropriate solar crown. It was then commonly referred to as the "Colossus solis". Nero's head was also replaced several times with the heads of succeeding emperors. Despite its pagan links, the statue remained standing well into the medieval era and was credited with magical powers. It came to be seen as an iconic symbol of the permanence of Rome. The emperor Constantine the Great remodeled the statue's face as his own.

Although the Colossus was preserved, much of the Domus Aurea was torn down. The lake was filled in and the land was reused as the location for the new Flavian Amphitheatre. Gladiatorial schools and other support buildings were constructed nearby within the former grounds of the Domus Aurea. Vespasian's decision to build the Colosseum on the site of Nero's lake can be seen as a populist gesture of returning to the people an area of the city which Nero had appropriated for his own use. In contrast to many other amphitheaters, which were on the outskirts of a city, the Colosseum was constructed in the city center, in effect, placing it both symbolically and precisely at the heart of Rome.

Although substantially ruined because of earthquakes and stone-robbers, the Colosseum is still an iconic symbol of Imperial Rome and was listed as one of the seven wonders of the World. It is one of Rome's most popular tourist attractions.

Sources:

Coarelli, Filippo (1989). Guida Archeologica di Roma. Milano: Arnoldo Mondadori Editore. ISBN 978-88-04-11896-1.
Elkins, Nathan T. (2019). A Monument to Dynasty and Death: The Story of Rome's Colosseum and the Emperors Who Built It. Baltimore, MD: Johns Hopkins University Press. ISBN 9781421432557.
Hopkins, Keith; Beard, Mary (2005). The Colosseum. Cambridge, MA: Harvard University Press. ISBN 978-0-674-01895-2.