Leonidas I (c. 530–480 B.C.) was a king of the city-state of Sparta from about 490 BC until his death in 480. The Spartans and associates defended the pass at Thermopylae against the Persian army Although Leonidas lost the battle, his death at Thermopylae was seen as a heroic sacrifice. Leonidas sent most of his army away when he realized that the Persians had outmaneuvered him. Three hundred of his fellow Spartans stayed with him to fight and die.

In 480 BC, the Persians with their king Xerxes attacked Greece. When the Greeks asked the Spartans to join their army against the Persians, the Spartans went to the Oracle at Delphi. The Oracle gave a prophecy. It said that either Sparta would fall or the Spartans would lose a king.

In August 480 BC, Leonidas went to Thermopylae with 300 of his bodyguards. Other Greek forces joined him there and formed an army of 4,000 soldiers. This army would try to hold the pass of Thermopylae against the great army of Xerxes I, King of Persia.

Leonidas and his men held Thermopylae for three days. On the third day, a Greek traitor named Ephialtes led the Persian army behind the Spartans. It was then that Leonidas sent away all the Greek troops except 700 Thespians, who refused to leave. The small Greek force was attacked from both sides. They fought hard but finally they were all killed. Xerxes told his men to remove Leonidas' head and put it on a stake. He also told them to crucify his body.

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