The Military Salute is a long-standing tradition of military forces around the world, and it is obviously the most visible and known gesture of military protocol to the average civilian. There is an urban myth that it evolved out of a custom in which mediaeval knights opened their visors with their weapon-hand to be recognised and to show that they were not armed; in fact it evolved from the former custom of men removing their hats as a sign of respect. This is the reason that in some military outfits (such as the US Marine Corps and Navy), it is incorrect to salute when you are not wearing a "cover." (In other outfits, customs are different, and salutes are given when bare-headed; meanwhile, in many armies, including the Russian one, it is expressly forbidden to salute without a hat on.) The salute evolved because of the introduction of headwear that could no longer be taken off easily with just one hand, especially bearskin caps and mitre-shaped grenadier caps. In the 18th century, when the military salute was first introduced, there were situations when it was still possible to give it with the left hand, e.g. on parade when the saluting officer was holding a spontoon in his right hand.