After further study and identification of this area as a quarry, it appears that this is one of a series of cuts into the bedrock associated with quarry machinery. This one, specifically, may have accommodated one of the posts to which cranes’ tie-rods were tied

Cut in tufo for a post. Remains of the post include the rocks (SU104) and the shape in the center of the cut where no rocks were present. The filling episode of the cut was post first, then rocks, then sediment.