title says it all really.
i'm talking about things like http://i.ytimg.com/vi/Js-13O2gscw/maxresdefault.jpg this

http://i.testfreaks.com/images/products/600x4...241838.jpg or this (yes i know the greathelm design is all over the map..)

helmets like those are constantly shown as being used by the teutonic order in popular art , why does everyone keep assuming they used them and is there any truth to it?

I don't think that they are too far fetched,but not in battle. It seems that artists and game developers have just applied the crests used in tourneys in their works to make them more appealing to the masses. They definitely look cool.

Blame Sergei Eisenstein's propagandist Alexander Nevsky from 1938 coupled with the Manesse Codex's depiction of Tannhäuser.



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As Phil mentioned they're most likely based on tournament crests.


http://manuscriptminiatures.com/4373/7053/

http://manuscriptminiatures.com/4121/8440/

All of the monastic military orders regulated the appearance of their brothers in an attempt to enforce piety. No personal adornment, rich clothing, personal arms, etc. were allowed. On the other hand, the fact that such prohibitions are continually passed and updated seems to indicate some monks were always pushing the limits. The medieval stereotypical parody of monks being overfed, over-sexed, and drunk undoubtedly has some basis in fact. Likewise, the RC Church banned tournaments routinely throughout the 12th and 13th centuries due to both the risk of strife among Christians, but also the party culture surrounding the events. But tournaments were continually held, even under the threat of excommunication. People don't always obey the rules.

There was some allowance for Masters and perhaps other leaders to show their status with some display, so it's possible that crests might have appeared on the helms of the Order's commanders. Despite the assertion that crests were only used in tournament, there are a number of battle depictions where crests are sometimes seen.

Still, I suspect the majority of brothers wore plain and unadorned helmets.