barbican vs fortification

barbican

noun
  • An opening in the wall of a fortress through which the guns are levelled; a narrow loophole through which arrows and other missiles may be shot. 

  • A tower at the entrance to a castle or fortified town 

  • A fortress at the end of a bridge. 

  • A temporary wooden tower built for defensive purposes. 

fortification

noun
  • That which fortifies; especially, a work or works erected to defend a place against attack; a fortified place; a fortress; a fort; a castle. 

  • A jagged pattern sometimes seen during an attack of migraine. 

  • The act of fortifying; the art or science of fortifying places to strengthen defence against an enemy. 

  • An increase in effectiveness, as by adding ingredients. 

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