I'm trying to work on a crest with a torse and mantle for my great helm, and so far I've been working towards a mid-13th Century kit. I came to the realization that I'm not actually sure how common such crests were in this century, since the examples I've seen may have instead been 14th Century tournament helms.

Does anyone know how early this practice began and how common it might have been (with regards to great helms)?

EDIT:
I guess I should clarify a little. I saw the Great Helm article here, and have googled around a little, and I realize that crests came into use in the 12th Century. I'm curious about the combination of torse and mantle, when that came into use, and how widespread these, and crests in general, were during the 13th, particularly mid-13th. Anyone know? Thanks! :)

Crests where known in the mid-13th century, but are not "common" in the same way that they would be in the early 14th c.

So, you COULD have one, but visually, you'll quickly end up being identified early 14th c, since there helmet crests are so iconic for that period.