I changed my mind - if I really want to do popular music, a through-composed, arhythmic Anglo-Saxon battle song is probably not the best way to start.
L'Homme Arme, on the other hand, is a mightily catchy little tune. It's described as a chanson, which implies that there are at least two other parts to it floating around somewhere. It's martial and warlike, and the original lyrics work just
fine, if they can be translated.
Challenge 1: Lyric translation that preserves something of the rhyme scheme of the original.
Challenge 2: Add two verses in a style consistent with 15th century Burgundian chansons. (Difficulty: Seems most chansons were love songs. Not sure how many other war songs there might be to examine style...)
Challenge 3: Document it.