It was built on a site just east of the Roman Forum, with construction starting between 70 and 72 AD under the emperor Vespasian. The amphitheatre, the largest ever built in the Roman Empire, was completed in 80 AD under Titus, with further modifications being made during Domitian's reign.
The Colosseum's name has long been believed to be derived from a colossal statue of Nero nearby.
This statue was later remodeled by Nero's successors into the likeness of Helios (Sol) or Apollo, the sun god, by adding the appropriate solar crown.
Nero's head was also replaced several times and substituted 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 Colosseum measures 48 metres (157 ft / 165 Roman feet) high, 189 metres (615 ft / 640 Roman feet) long, and 156 metres (510 ft / 528 Roman feet) wide, with a base area of 6 acres. Unlike earlier amphitheatres, it was an entirely free-standing structure, constructed on flat ground rather than being built into an existing hillside or natural depression.
Its outer wall originally measured 545 metres (1,788 ft / 1,835 Roman feet) and is estimated to have required over 100,000 cubic meters (3,531,466 ft³) of travertine stone held together by 300 tons of iron clamps. However, it has suffered extensive damage over the centuries, with large segments having collapsed following earthquakes.
The north side of the perimeter wall is still standing; the distinctive triangular brick wedges at each end are modern additions, having been constructed in the early 19th century to shore up the wall.
The remainder of the present-day exterior of the Colosseum is in fact the original interior wall.
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