I can't think of what sort of music exactly but here is some stuff that I hope would inspire good Bretonnian music. The first three are from the movie Excalibur which is about the arthurian legends which are the basis for the Bretonnians. I'm not suggesting you use any of these exactly but I hoping they will inspire you.

The inspiration music in this clip starts at 1:34 but do watch the whole clip

http://ca.youtube.com/watch?v=PjV94_...eature=related

This one would make good battle music

http://ca.youtube.com/watch?v=NOqlV4Le9Tk

http://ca.youtube.com/watch?v=2gludr...eature=related

Some other clips

https://www.youtube.com/watch?v=n0sE...eature=related

https://www.youtube.com/watch?v=OHIW...eature=related

These two are from Kingdom of Heaven

https://www.youtube.com/watch?v=-oO6pCRe3pM

https://www.youtube.com/watch?v=cA0K...eature=related

Also I suggest you listen to the Kingdom of Heaven soundtrack which can be downloaded here

http://isohunt.com/torrent_details/1...ck?tab=summary

Or watch the movie, or listen to the soundtrack and watch the movie.