casern vs garrison

casern

noun
  • A lodging for soldiers in a garrison town (formerly usually near the rampart); a barracks. 

garrison

noun
  • The troops stationed at such a post. 

  • A permanent military post. 

  • Occupants. 

  • A military unit, nominally headed by a colonel, equivalent to a USAF support wing, or an army regiment. 

verb
  • To convert into a military fort. 

  • To occupy with troops. 

  • To assign troops to a military post. 

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