Originally covered by slab 5669, which blocked access to this drainage shaft, except for water. This vertical shaft must connect to horizontal subterranean drainage channels.
Opening/access to cistern. It is perhaps connected to a negative feature (the same cistern?) discovered under the slab floor in room 16 (SU 5662).
Built structure of small tufo slabs within drain south of 5600 (5751) and Rectilinear cut in bedrock associated with 5600 and 5751 (5752)