The underground structure below the Colosseum’s arena is called the Hypogeum.
The name comes from Greek roots meaning “underground.” The Hypogeum was a two-level network of tunnels, corridors, cages, lifts, and service spaces beneath the wooden arena floor. It allowed performers, animals, scenery, and equipment to be kept out of sight before spectacles began.
Emperor Domitian ordered the subterranean complex after the Colosseum’s initial construction. Vertical shafts and mechanical platforms enabled animals and scenery to appear suddenly through trapdoors, creating dramatic effects for spectators. Tunnels also connected the arena area with nearby facilities, including the gladiators’ training school, the Ludus Magnus.
The Hypogeum ended the possibility of regularly flooding the arena for mock naval spectacles, though the practicality of earlier water displays remains debated. It is not the same as catacombs, which generally refers to underground burial networks. Today, the exposed Hypogeum is one of the clearest ways to see how the Colosseum’s spectacles operated behind the scenes.