Exterior wall of the earlier area F structure as evidenced by the lack of abutting walls on the western face. The general purpose of this structure remains unknown pending further excavation. The relationship between SU 5156 and SU5157 is obscured by a later concrete repair, thus we cannot say with certainty which abuts the other without exposing more of the walls. Several patches of mortar may represent later repairs, similar to wall SU 5009.