A layer of preparation, consisting of crushed tufo chips, for the leveling and foundation of a slab floor in the northern corridor around the landing of the staircase (i.e. the hypothetical eastern continuation of slab floor 5522, which has been robbed).
A floor prep layer composed of compact silt and crushed tufo for the pavement of northern corridor.
Fill for floor prep under tufa slabs (Fs) and bedrock