The Roman Legions - Greatest Killing Machines The World Had Ever Seen

In reference to the early Roman Kingdom (as opposed to the Roman Republic or empire), "the legion" means the entire Roman army. The subsequent organization of legions varied greatly over time but they were typically composed of around five thousand soldiers, divided into three lines of ten maniples during the republic, and later into ten cohorts during the early empire.
https://www.youtube.com/watch?v=KJ7U107xvu8