The Colosseum or Coliseum, originally known as the Flavian Amphitheatre (Latin: Amphitheatrum Flavium), is the largest amphitheatre built in the Roman empire. Originally capable of seating 50,000 spectators, it was once used for gladiatorial combat. It was built in the 70s AD by Jewish slaves captured at the end of the Great Jewish Revolt.
See en.wikipedia.org/wiki/Collosseum for more detail.