breastwork vs murus

breastwork

noun
  • A parapet. 

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

  • Breast augmentation. 

  • A railing on the quarter-deck and forecastle. 

murus

noun
  • A wall. 

  • A pattern-forming ridge on the surface of a pollen grain. 

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