15031 is later than 15051, even if it does not cover it directly. Irregular alignment abutting both 15051 and 15032. Seems not to have been very high originally, because facing and core (same stones but oriented differently) do not connect well- hence limited structural strength.
Come da 57 ad essere coperta da 31 se appoggia a 51 che i coperto da 04 che viene prima di 31?
SU 15057: view toward west