 The battle begins soon after the Spartans ' refusal to lay down their weapons . Using the Hot Gates to their advantage , plus their superior fighting skills , the Spartans repel wave upon wave of the advancing Persian army . During a lull in the battle , Xerxes personally approaches Leonidas to persuade him to surrender , offering him wealth and power in exchange for his allegiance ; Leonidas declines and mocks Xerxes for the inferior quality of his fanatical warriors . In response , Xerxes sends in his elite guard , the Immortals , later that night . Despite some Spartans being killed , they heroically defeat the Immortals ( with slight help from the Arcadians ) . On the second day , Xerxes sends in new waves of armies from Asia and other Persian city @-@ states , including war elephants , to crush the Spartans once and for all , but to no avail . Meanwhile , Ephialtes defects to Xerxes to whom he reveals the secret path in exchange for wealth , luxury , and ( especially ) a uniform . The Arcadians retreat upon learning of Ephialtes ' betrayal , but the Spartans stay . Leonidas orders an injured but reluctant Dilios to return to Sparta and tell them of what has happened , a " tale of victory " . 
