battlements

Noun

battlement (plural battlements)

1. 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.
   • Towers, and battlements it sees
     Bosom'd high in tufted trees,
     Where perhaps some beauty lies,
     The cynosure of neighbouring eyes.1645, John Milton, L'Allegro

   Synonyms:

   crenellation

2. Any high wall for defense.
3. (poetic) The towering roof of heaven.