When the Hippodrome was constructed a slope at its southwestern side had to be brought to the level of the hippodrome grounds. In order to do so a large and high wall containing 25 cells, covered by vaults, were constructed. A corridor connects them. It cannot be visited, but its position is known. A vocational school stands on the platform nowadays, formerely a bath and mill stood there.

This is one of some pictures I took of the construction, called Sphendon.