Like many complex monuments, nuraghe Losa has an outer wall with towers, called antemural. In this case the antemural does not surround the whole bastion but is limited to its rear part. It is possible that the antemural of nuraghe Losa was never completed or that it was mostly removed. Two long rectilinear walls are preserved, with slits for observation or defence and two towers at the corners (F, G). Towers F and G also have circular rooms with many slits, originally covered by corbelled domes. Under the inner wall of tower F there is a water cistern. The rectilinear wall leans against the trilobate bastion forming a backyard (E) roughly trapezoidal in plan, which is reached through a small entrance.
