battlement vs redoubt

battlement

noun
  • 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. 

  • Any high wall for defense. 

redoubt

noun
  • A reinforced refuge; a fort. 

  • A small, temporary, military fortification. 

  • The return of doubt. 

  • A place of safety or refuge. 

verb
  • To fortify, to make into a stronghold. 

  • To doubt again. 

How often have the words battlement and redoubt occurred in a corpus of books? (source: Google Ngram Viewer )