An ancient open-air theatre in Rome, Italy, built in the closing years of the Roman Republic. It was named after Marcus Marcellus, Emperor Augustus's nephew, who died five years before its completion. Space for the theatre was cleared by Julius Caesar, who was murdered before it could be begun; the theatre was so far advanced by 17 BCE that part of the celebration of the ludi saeculares took place within the theatre; it was completed in 13 BCE and formally inaugurated in 12 BCE by Augustus. The theatre was 111 m in diameter; it could originally hold 11,000 spectators. The ruins were gradually built on top of and integrated into apartments. The ruins have been studied by generations of architects.