SU 5530 is a concrete construction including tiles, basalt, small tufo blocks, covering 5460, abutting 5453 and 5451. This SU supports 5452 (probably re-used from elsewhere) and seems to be contemporaneous with the construction (wedges 5499) of threshold 5451 to create a cohesive Southern limit of ROOM 15 (maintaining the orientation of a previous phase represented by 5460 and 5453 as well as probably re-using materials within the concrete and 5499, and the blocks for 5452 and 5451.