These slabs of tufo cover the drainage channel that comes in from Room 21. While in Room 21 the drain runs along the E wall, in room 22 it goes diagonally from the NE corner to the center of the room. The slabs would have been under the floor level of the room while in use, and we have evidence of continuous mortar repairs on and along the slabs. This is possibly due to the far south nature of their location, at the bottom of the hill.