The Flavian Amphitheater (the original name) was inaugurated in the year 80 AD after 8 years of hard work and financed by the treasures of the Siege of Jerusalem (70 AD) led by the general Titus who will become Emperor after his father’s death.
After two years the Emperor Domitian (Titus’ brother) had the tunnels digged under the arena to be used as the backstage where the fierce beasts could suddenly be lifted from. Its corridors and rooms were used for the preparation of the shows and as the waiting area where to keep costumes, animals and settings for the Romans’ entertainment.
The arena (a latin word which means sand) could be filled with water (before the underground was digged) to organize sea battles (naumachiae) thanks to the aqueduct built by Nero for his Golden House and reenact important past events.
Below You can see those sections most visitors do not see since a special exclusive ticket plus a view from the third level where the lower class used to sit.
Maurizio Rome Guide 