The Origin of The Military Salute

According to modern military manuals, the modern western salute originated in the Middle Ages when knights who greeted each other raised their visors to show their faces, using a motion that resulted in what looks like a modern salute. Their helmets were equipped with protruding pins on the visors to allow the visors to be lifted using the saluting motion. The origin accounts for the common rule of not saluting when not wearing something on your head, as the salute was originally performed only when wearing a helmet (Wikipedia).