quarterdeck vs stronghold

quarterdeck

noun
  • The aft part of the upper deck of a ship; normally reserved for officers 

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 quarterdeck and stronghold occurred in a corpus of books? (source: Google Ngram Viewer )