Under Xerxes I, the Persian army moved south through Greece on the eastern coast, accompanied by the Persian navy moving parallel to the shore. To reach its destination at Attica, the region controlled by the city-state of Athens, the Persians needed to go through the coastal pass of Thermopylae (or the “Hot Gates,” so known because of nearby sulfur springs). In the late summer of 480 B.C., Leonidas led an army of 6,000 to 7,000 Greeks from many city-states, including 300 Spartans, in an attempt to prevent the Persians from passing through Thermopylae.
Leonidas established his army at Thermopylae, expecting that the narrow pass would funnel the Persian army toward his own force. For two days, the Greeks withstood the determined attacks of their far more numerous enemy. Leonidas’ plan worked well at first, but he did not know that there was a route over the mountains to the west of Thermopylae that would allow the enemy to bypass his fortified position along the coast. A local Greek told Xerxes about this other route and led the Persian army across it, enabling them to surround the Greeks. Much of the Greek force retreated rather than face the Persian army. An army of Spartans, Thespians and Thebans remained to fight the Persians. Leonidas and the 300 Spartans with him were all killed, along with most of their remaining allies. The Persians found and beheaded Leonidas’ corpse–an act that was considered to be a grave insult.