In architecture, crenelation is the indented or notched construction of the battlements atop a wall; a crenelated wall is one topped with merlons ? pieces of wall protecting defenders who looked through and used their weapons through the notches, or crenels. Crenelation is most typically located on a fortification's parapet. see thumbnail to leftHere are three of the possible shapes of crenelation.Also see arms and armor, corbel, embrasure, masonry, and splayed opening.