N-S running wall E of tufo paving slabs and bound to E-W running wall 4056 on N. Tufo ashlar construction, probably the same as 4056 with two rows of tufo blocks sandwiching a tufo rubble fill. W row of blocks missing, however--would have covered tufo slabs 4055, possibly explaining the raised lip on the E side of the slabs here. 4056 and 4057 of uncertain purpose, but seem to form a boundary between the tufo slabs 4055 to the W and the as-yet-unexcavated area to the SE.