This single ashlar block (together with the smaller block 5587 to the south) divides two tufo slab floors from one another - 5595 to the east and 5739 to the west. Both of these floors appear to serve a double purpose as covers for the drainage channel that is known to run east-west on this line through the complex. Interpretation of this block is made more difficult by the incomplete preservation due to robbery activity of the original occupation levels of Room 16 to the north. The end of the slab floors as preserved now coincides with the end of the block, but it is unclear whether either (or both) extended further north into the main space of Room 16. If tufo block 5596 to the east represents an original entrance into this space, then movement and the line of sight westward would have been almost immediately impeded by this feature, if it was a wall rising to a full height. It seems unusual that one would enter the space onto the slab floor 5595, and be immediately forced to turn right to enter the main part of the room (or another room) for no apparent reason, since presumably the floor/drain cover could have, in theory, continued uninterrupted to join with 5739 to the west. Two possibilities exist: either the slab drain cover and this block are not part of the original phase of the complex, and are related to a later reorganization of the space (unlikely, for a number of reasons), or this wall served a purpose that is now beyond our ability to reconstruct with any certainty. The hints of a finished surface on the top of block 5587 are tantalizing but ambiguous, and could seemingly support either hypothesis at this point. One further consideration is necessary: evidence from the western wall of Room 16 (see SU 5665) and the layers north of and below the slab floor drain covers (see SU 5780) suggests that there was probably an ashlar wall that ran east-west at the northern limit of this block from wall 5565 at the west of Room 16 to threshold 5596 at the east of the slab floor 5595. Thus the space of these two slab floors (5595 and 5739), divided by this block, would have been separated, at least partially, from the rest of Room 16 to the north.