After study, it appears that this was one a series of fills of a drainage channel in the area.

Possibly the incomplete remains of the foundation of a wall, in which case cut SU510 would be the construction trench for the wall. To the east, SU539 may be a continuation of this wall. Due to gaps on either side of SU535 in the stone packing and to the complete absence of similar stone-packing to the W (in the area of SU532), and to the varying width of SU510 along its length, the interpretation of SU535 (and SU539) as wall foundations remains fragile.