1) Battlement 2) Bulwark 3) Crenelation 4) Rampart 5) Wall 1) Battlement 2) Crenelation 
The arrangement of battlements into a line of alternating merlons and crenels.
A sequence of alternating raised and lowered wall sections at the top of a high exterior wall or parapet. Crenellations were originally employed for defensive purposes (one could hide behind a raised wall section, while shooting down at enemies from over a lowered wall section), but were later used for decoration. Also known as a battlement.
fortification- a 'license to crenellate' was official permission to raise a fortified building or fortify an existing structure. Jagged protective stonework at the top of a castle wall
With battlements or loopholes
The treatment of a parapet wallhead as in a mediaeval castle, with tall and short sections alternating. Common in early Gothic Revival churches. Related Words: Gothic (revival); Parapet; Wallhead
parapet on top of a castle wall, with a series of gaps (embrasures or crenelles) between raised portions (merlons), allowing defenders to shoot through; also called battlements
Square openings in the top of a parapet 
crenellation 1. The action of constructing ramparts with gaps for firing guns or arrows. 2. A rampart built around the top of a castle with regular gaps for firing arrows or guns.
parapet on top of a castle wall, with a series of gaps (embrasures or crenelles) between raised portions (merlons), allowing defenders to shoot through; also called battlements