Once closed down and locked up by Zeus due to the senseless violence, it was reopened when Sora opened the lock during his first visit to Olympus Coliseum. Hades knew Sora would 'play hero' and save Megara so that the Underdrome would be reopened. Hades then decided to use the Underdrome to pit Auron and Hercules against each other much like he wished to do with Cloud in Kingdom Hearts.