Crushed tufo preparation with remnants along eastern and southern edges of smoothed mortar/ceramic/stone floor surface associated clearly with later concrete walls and remnants of plaster on lower eastern wall. Floor appears to run on top of lower southern wall (threshold of SU5351) and thus may have continued south. This "top" floor surface clearly runs over ashlar blocks in the northern limit (and "rubble" feature as well as possible drain in N-W corner).