fort vs garrison

fort

noun
  • Any permanent army post. 

  • An outlying trading-station, as in British North America. 

  • A structure improvised from furniture, bedding, etc., for playing games. 

  • A fortified defensive structure stationed with troops. 

verb
  • To create a fort, fortifications, a strong point, or a redoubt. 

garrison

noun
  • A permanent military post. 

  • The troops stationed at such a 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 fort and garrison occurred in a corpus of books? (source: Google Ngram Viewer )