This tufo slab, associated and integrated with the slab floor drain cover 5595 immediately to the west, appears to have served as the threshold to enter the western half of Room 16 from the eastern half. It also seems to represent the northern continuation of the line of ashlar wall 5551. This threshold is a key piece of evidence that seems to suggest that the line of N-S wall 5551 continued north through Room 16, though this hypothetical wall has now been robbed; thus this would suggest that Room 16 should properly in the original phase be divided into two separate rooms (see also interpretation of SU 5545 and 5561). This would have been an (the?) entrance into the western room from the eastern. The nature and purpose of the space into which this threshold opened to the west - paved by slabs 5595 and delimited by walls 5574 and 5586, as well as the hypothesized wall that would have run along the northern limit of 5595 - is uncertain at this time.