The Colosseum is the largest ancient amphitheater ever built, and is still the largest standing amphitheater in the world, despite its age.

Construction began under the emperor Vespasian (r. 69–79 AD) in 72 and was completed in AD 80 under his successor and heir, Titus (r. 79–81). Further modifications were made during the reign of Domitian (r. 81–96). The three emperors who were patrons of the work are known as the Flavian dynasty, and the amphitheater was named the Flavian Amphitheatre by later classicists and archaeologists for its association with their Flavius family name.

The name Colosseum is believed to be derived from a colossal statue of Nero on the model of the Colossus of Rhodes. The giant bronze sculpture of Nero as a solar deity was moved to its position beside the amphitheater by the emperor Hadrian (r. 117–138). By the year 1000, the Latin name "Colosseum" had been coined to refer to the amphitheater from the nearby "Colossus Solis".

The Colosseum is built of travertine limestone, tuff (volcanic rock), and brickfaced concrete. It could hold an estimated 50,000 to 80,000 spectators at various points in its history, having an average audience of some 65,000; it was used for gladiatorial contests and public spectacles including animal hunts, executions, reenactments 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.

Although substantially ruined by earthquakes and stone robbers taking spolia, the Colosseum is still a renowned symbol of Imperial Rome and was listed as one of the New 7 Wonders of the World. It is one of Rome's most popular tourist attractions and has links to the Catholic Church, as each Good Friday the Pope leads a torchlit "Way of the Cross" procession that starts in the area around the Colosseum. The Colosseum is depicted on the Italian version of the 5 euro cent coin.