This is a mortar surface in the eastern part of our floor sondage. It seems to run along the center of the rooms, starting from close to where the two drains would connect in room 22, and continuing to the S towards where the threshold (5823) is. This SU draws particular attention due to another mortar covered patch immediately to the S of threshold 5823. It could possibly be a mortar patch laid to perform & cover drainage repair work in antiquity. A drain similar to those to the north could possibly continue to the south onto and/or past the Via Gabina.