put somebody to the swordto kill someone with a sword
put to the swordKILL, execute, put to death, murder, butcher, slaughter, massacre, cut down, slay
 [TahlilGaran] Dictionary of Contemporary English ▲
 put to the sword v. phr., 
literary To kill (people) in war, especially with a sword. 
 The Romans put their enemies to the sword.
 The Romans put their enemies to the sword.  In some wars captives have been put to the sword.
 In some wars captives have been put to the sword.  [TahlilGaran] English Idioms Dictionary ▲