The vast network of rooms, cells, tunnels and passages under the Roman Colosseum is called the Hypogeum, from the Greek words hypo (meaning under) and gaia (meaning earth). The hypogeum was not part of the original construction but was built by Emperor Domitian, the younger son of Emperor Vespasian. The addition of the hyypogeum meant that water battles at the Colosseum would no longer be possible.
The hypogeum was covered by an arena of 83 meters by 48 meters (272 feet by 157 feet), compromised of a wooden floor covered by sand (the Latin word for sand is harena). The original arena floor is long gone making the hypogeum clearly visible from the tiers above.
The Colosseum underground consisted of a two-level subterranean network of tunnels, shafts, mechanical devices and animal cages. The tunnels led to nearby stables and the gladiators’ barracks outside the Colosseum so animals and performers could easily be brought inside. Separate tunnels that lead to the Imperial Palace were provided for the Emperor and the Vestal Virgins to enable them to enter the Colosseum without needing to pass through the crowds.
The cages in the hypogeum housed the wild animals required for the contests and shows of the day. The vertical shafts contained lifts operated by ropes and pulleys which led directly to the arena providing instant access for fast changes to scenery, animals and occasionally convicts and gladiators.
Conditions underground must have been extremely difficult. The excrement of the animals and the stench of blood and death would have filled every part of the hypogeum. In summer the heath must have been almost unbearable while lamps would have burnt continuously as the hypogeum had very little natural light. The slaves, convicts and gladiators would clearly be able to hear the screams of the crowds, roars of the animals and shouts of terror and agony from the violence above their heads.