Degraded tufo floor preparation, likely for a mosaic floor similar to that in room 2, part of the same phase as 5347, 5345, 5342, 5344, 5383, and 5319. Likely a covered space, perhaps a kind of portico outside rooms 3 and 4. Relationship to 5321 is unclear because this surface is not preserved at the interface with the tufo slab floor, but 5321 was likely put in place first as part of the same phase, since it seems that the original extent of this surface would have covered the fill of the cut in the bedrock that seems to have been made to accommodate floor 5321 (SU 5490).