Any high wall for defense.
In fortification: an indented parapet, formed by a series of rising members called cops or merlons, separated by openings called crenelles or embrasures, the soldier sheltering himself behind the merlon while he fires through the embrasure or through a loophole in the battlement.
The towering roof of heaven.
A place built to withstand attack; a fortress.
A place of domination by, or refuge or survival of, a particular group or idea.