The Colosseum is named after a statue that is long gone.
The building went up between roughly 70 and 80 AD and held 50,000 to 80,000 spectators. In antiquity it was simply called the amphitheatre. The name Colosseum appeared only around the year 1000 – after the Colossus, a giant bronze statue of Nero that Emperor Hadrian had moved beside it.
Useful: A building's name often says more about later ages than about its builders.
Source: en.wikipedia.org