Underground of the Colosseum

The elliptical shape of the Colosseum was realised using a sophisticated 4-centred geometric procedure and was also taken up by the arena floor by adopting a masonry mixed with a wooden planking that was covered with sand. Under the arena's planking were spacious underground service rooms that were built after the Emperor Domitian.

Previously, the arena could be flooded to host naumachiae or shows with swimmers, as reported by Martial in his book De spectaculis. A large part of the dungeon is still visible today from above and one can see a wide corridor along the major axis that divides the area into two lateral semicircles traversed by twelve curvilinear corridors. Along the perimeter wall are a series of vaulted service rooms that probably housed the animals used during the games, together with scenery.

The corridor along the main axis of the ellipse ended with two galleries that open inside the concrete donut forming the foundations of the amphitheatre. Two other galleries along the minor axis of the ellipse, one in the direction of the Colle Oppio and one in the direction of the Caelian, have not yet been excavated. A fifth tunnel, located along wedge V below the imperial stage, was built in Domitian times and was probably an access route reserved exclusively for the emperor and directly connected to some imperial buildings in the area of the Temple of Claudius on the Caelian.