It is a Latin word, first coined in the third century AD, meaning "Roman-ness" and has been used by modern historians as shorthand to refer to Roman identity and self-image.
Prior to the formation, under Gaius Marius, of the standing Roman Army, Rome had a militia-type defence-force which could be called up in time of war and then disbanded during peacetime.
According to Roman legend, Cincinnatus was tending his farm when a messenger arrived, telling him that Rome was under attack and that he had been elected dictator.
He defeated the enemy tribe within a matter of weeks and, despite there remaining most of his six-month term as dictator with absolute power, returned to his farm.
Because of the widespread influence of Roman classical literature, the idea of the homo militaris also took root in colonial and early United States.