ballpoint pen vs gladius

ballpoint pen

noun
  • A pen, similar in size and shape to a pencil, having an internal chamber filled with a viscous, quick-drying ink that is dispensed at the tip during use by the rolling action of a metal sphere (around 0.7 mm to 1 mm in diameter). 

gladius

noun
  • A pen, a hard internal bodypart of certain cephalopods, made of chitin-like material. 

  • A Roman sword roughly two feet long. 

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