In Sparta, his fellow king Leotychidas is fighting a losing battle with the Ephors over the religious harvest festival of Carneia that is due to take place, with members of the council arguing that the army should wait until after the festival is over before it marches, while Leotychidas fears that by that time the Persians may have conquered Greece. After this, Leonidas learns of the Persian advance and travels to Sparta to spread the news and rally the rest of the troops. Outside the hall, Leonidas and Themistocles agree to fortify the narrow pass at Thermopylae until the rest of the army arrives. In Corinth, Themistocles of Athens wins the support of the Greek allies and convinces both the delegates and the Spartan representative, warrior king Leonidas I, to grant Sparta leadership of their forces. Accompanying him are Artemisia, the Queen of Halicarnassus, who beguiles Xerxes with her feminine charm, and Demaratus, an exiled king of Sparta, to whose warnings Xerxes pays little heed.
King Xerxes of Persia leads a vast army of soldiers into Europe to defeat the small city-states of Greece, not only to fulfill the idea of " one world ruled by one master", but also to avenge the defeat of his father Darius at the Battle of Marathon ten years before.