Parapet (portion above the roof) of the exterior wall of a fortification, consisting of alternating low portions (crenels) and high portions (merlons).
Rooftop defenders would shoot from behind the merlons during times of siege. Medieval battlements were often bracketed out (see corbel ) to form a machicolation (overhang) with holes in its floor through which objects could be dropped on encroachers below.