The Canterbury Tales: The Knight's Tale
Palamon and Arcite
If Palamon and Arcite are the protagonists, then that means that they also have to be the antagonists. Why? Well, both men want Emily, and the only thing that's standing in their way is the other guy. So Palamon and Arcite have to duke it out in a duel and finally, an epic joust, that decides who will win her. Since the tale doesn't really allow us to take sides, both Palamon and Arcite are as equal as antagonists as they are as protagonists.