IL COLOSSEO UNDERGROUND
The floor of the arena rested on lofty substructures, consisting of walls, some of which follow the elliptical curve of the building, while others are parallel to the major axis. The east half of the arena has been excavated so that these substructures substructures are visible. They are entered by four subterranean passages, on the lines of the major and minor axes. Commodus constructed another subterranean passage, a sort of crypto-porticus, which starts a little to the east of the state entrance on the south side, and leads to the buildings of Claudius on the Caelian. This was for his own use, when he visited the amphitheatre. In the substructures are traces of dens for wild beasts, elevators, and mechanical appliances of various sorts, but their principal object must have been to provide for the drainage of the water, which flows so abundantly into this hollow, and which was carried off in a sewer l connecting with that beneath the modern via di S. Gregorio. The masonry of these substructures dates all the way from the first century to the end of the fifth.