The tufo block ashlar wall forms the western boundary of rooms 20 and 21. It is bound by mortar and in the southern portion sits above the opus reticulatum construction, 5814. The ashlars thus appear to have been reused from the walls of an earlier phase, perhaps the red tufo ashlar walls just to the north of Room 20, which have clearly been spoliated. The wall therefore relates to a fairly late occupation phase in this area.