Answer:
A Parapet
The battlement can be used in general reference to a location possibly during a battle or siege. Another more elegant and synonymous name describing a sawtooth shaped parapet is crenelation. The crenelation is made up of merlons (the high part protecting shooters) and crenels (the low part exposing shooters)
A crenelation is usually found protecting an allure (wall walk) on the outer wall.