Finding a Medieval song

Can anybody help me finding a particular medieval song (or I think it's medieval anyway)? The beginning of the song is used in Civilization IV when Christianity is founded (see attachment 1) and it is also used in the TV show 'Medieval Lives' by Terry Jones. I don't know if I'm allowed to post a link to the episode (if not, you can always google it), but if you want to hear it, watch 'the Monk' episode. It appears around 5:34.

Bump?

Dunno. I know some of the music used while playing though, like this:

Yeah, but it wasn't a full song, only that part you hear when converting...

You can also hear the song here (5:34):

http://www.veoh.com/collection/Archa...808314hRNcbFd5

That link is probably not legal, if so I'll delete it. But I really want to know which song is it.

Edit: can someone make out what exactly they're singing? Exalt..., rex alt...?