SU 5400 is a rubble wall that corresponds to an earlier phase of room 9 associated with floor 535 and earlier levels north predating the northward extension of the room represented by the conservation of cement wall 5348 (associated with cement walls 5349, 5350, 5351 and floor 5320). The wall clearly reused building materials, particularly basalt slabs and was truncted by cut 5352. Further excavation may reveal how it is related to tufo features 5485 and 5321, its western limit (excavation limit of 5320, 5355, etc.) and its eastern limit (under 5321, 5349).