battlement vs breastwork

battlement

noun
  • The towering roof of heaven. 

  • 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. 

  • Any high wall for defense. 

breastwork

noun
  • A parapet. 

  • A fortification consisting of a breast-high bulwark; a parapet. 

  • Breast augmentation. 

  • A railing on the quarter-deck and forecastle. 

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