What is the name of that famous song played in all those trojan, roman, spartan (etc.) war movies?

I was at the dodger game on 6/29/09 when they played the mariners, and heard a song that is incredibly famous. It is played in all those war movies, (spartan, roman, etc.). It is an intense chant from a choir. I was wondering what the name of it was and who sings it.