The playing area itself consisted of an oval measuring 75 by 44 meters, but it was actually a wooden platform covered with a layer of sand. Beneath this surface was a complex system of tunnels and cells known as the hypogeum, used to house gladiators, prisoners and animals. The floor of the arena had several trap doors and hoists that connected to the basement and could be used during the development of the shows.

The arena design included a sophisticated drainage system that connected through four wide sewers. Initially, it has been suggested that these sewers were designed to evacuate water after the naval events that used to take place. However, it seems that during the reign of Domitian, the idea of naumachiae was abandoned and the sewers were paved to allow the use of forklifts in gladiatorial combats. Today, the wooden cover that once existed is no longer preserved, leaving the entire intricate subway labyrinth exposed to the open air.