Hyperion wants to get a magical weapon called the Epirus Bow and use it to free the Titans, whom the Greek Gods imprisoned after an ancient war. Opposing him is Theseus, a peasant, and his ragtag band of comrades.
Theseus finds the bow, but Hyperion captures it and goes to the mountain where the Titans are captive. He uses the bow to break through the Greek army's defences and succeeds in releasing the Titans. The Gods come down to Earth and fight the Titans, killing many of them and losing several Gods in the process. Finally Zeus yanks on two huge chains that literally collapse the whole mountain on top of them - the surviving Gods zip back up to the heavens, escaping as the Titans are buried.
Theseus fights with Hyperion and kills him, but is wounded. Just as he dies he zaps off to heaven himself.
The film ends with Theseus's son having a vision of his father amongst the Gods, fighting great battles in the clouds.