Wall 5545 appears to form the northern limit of Room 16. The plaster on the southern face of the wall seems to indicate an interior space. The U-shaped cut in wall is a niche that could have accommodated an engaged column or another architectural feature (lararium, e.g.?). The change in alignment matches up with western limit of monumental staircase. This change before resuming running E-W could have provided for more space in the room in front of the stairs. The cut in the central block of 5545 supports the theory that originally Room 16 may have been divided by a wall (continuing the line of wall 5551 to the south) between slab floors 5661 and 5662, as it lines up with a cut in the bedrock that spans NS through the room. Thus Room 16 may have been two separate rooms, and the working of this central block of wall 5545 may have been to accommodate a kind of interlocking ashlar construction.