The plot revolves around King Leonidas, who leads 300 Spartans into battle against Persian "god-King" Xerxes and his army of more than one million soldiers. As the battle rages, Queen Gorgo attempts to rally support in Sparta for her husband. The story is framed by a voice-over narrative by the Spartan soldier Dilios. Through this narrative technique, various fantastical creatures are introduced, placing 300 within the genre of historical fantasy.