citadel vs mirador

citadel

noun
  • A strong fortress that sits high above a city. 

  • A stronghold or fortified place. 

  • An armoured portion of a warship, housing important equipment. 

  • A Salvation Army meeting place. 

mirador

noun
  • a tower that offers a panoramic view 

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