parapet vs stronghold

parapet

noun
  • A fortification consisting of a wall. 

  • Part of a perimeter that extends above the roof. 

  • A low protective wall. 

  • Hyponym: balustrade 

stronghold

noun
  • A place built to withstand attack; a fortress. 

  • A place of domination by, or refuge or survival of, a particular group or idea. 

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