Probably post-abandonment accumulation in construction cut for the placement of the three tufo blocks (5397) placed at northern extent of course of wall 5337. Large red tufo fragment of block has fallen into construction cut. Opening to drainage feature exposed by the removal of this layer approximately 15 feet deep, visible under block at NW corner of cut. Due to the position of collapse of block and presence of drain, the cut was likely empty for drainage. Accumulation only occurred after robbing of the tufo pavement (5410; robbery = 5420).