The Roman Colosseum or Coliseum, originally known as the Flavian Amphitheatre, was commissioned in AD 72 by Emperor Vespasian. It was completed by his son, Titus, in 80, with later improvements by Domitian.
The Colosseum is located just east of the Roman Forum and was built to a practical design, with its 80 arched entrances allowing easy access to 55,000 spectators, who were seated according to rank. The Coliseum is huge, an ellipse 188m long and 156 wide. Originally 240 masts were attached to stone corbels on the 4th level. Source: rome.info