Does the metal “plume” on the top of the helmet have a functional purpose? I would think that thing would be heavy as it is without adding metal decoration.
I think it’s supposed to mimic the crests that were used on Assyrian, Urartian, Persian, and eventually Greek and Roman helmets.
SOME helmet crests and/or points do serve a purpose. The most common being to deflect blows from above. Usually this can be accomplished by simply rotating the head. The danger of this tactic is that the blow can often slide down to the shoulder with enough force to damage.
The crusader flat top helm (called a pot helm) has a flat top and does not deflect blows. It was not that effective against hammer based weapons.
Like the “bear skin” hats worn by British troops, the wide epaulettes (still used in many dress uniforms), the exaggerated hats worn by many tin-foil dictators
.. ALL such plumes and hats and decorations add to the bear’s height, shoulder width, and impression of strength and courage to the foes a few yards before battle. And, the wide cover does protect the head somewhat, and these were worn for the short tournament battles, not for long marches over months of countries in remote provenances.
And - as Napoleon said - morale is to material as 10 is to 1. If a soldier feels taller, stronger, braver, wider, better than his weak, short, little opponent, he WILL be better, stronger, more formidable in battle.
To stop the head inside from being split open by a blow from a sword or battle axe to the top of the helmet.