The Flavian Amphitheater at Pozzuoli is the third-largest Roman arena ever built, after the Colosseum in Rome and the amphitheater at Capua, with a capacity estimated at around 40,000 spectators. Construction was completed under Vespasian and Titus in the late 1st century AD, and the building served as the main venue for gladiatorial games in the Puteoli colony, which was then one of the most important port cities in the Roman world.
What makes Pozzuoli's amphitheater particularly worth visiting is the condition of the underground passages — the hypogeum — beneath the arena floor. At the Colosseum, most of the floor has been removed and the hypogeum is exposed; here, the floor is largely intact, and you can walk through the vaulted underground corridors where animals and gladiators waited before entering the ring. The trapdoors and lifting mechanisms for raising animals into the arena are still visible. It is a vivid illustration of how these spectacles actually worked.