In the summer of 480 B.C., anywhere from 5,000 to 20,000 Greek hoplites under the command of King Leonidas of Sparta and commander Demophilus of Thespiae marched North to protect the pass of Thermopylae. The Persian army, alleged to contain 300,000 soldiers, among them were 10,000 Immortals, arrived at the pass of Thermopylae in late August or early September. The outnumbered Greeks held off the Persians for one week (seven days [including three of battle] ) before the rear-guard faced extermination. King Leonidas, knowing that he was to be annihilated by the Persians, ordered the majority of the Greek army to join the Athenians and remained to guard their retreat with 300 Spartans, 700 Thespians, 400 Thebans. The Persians must therefore retreat or advance,and advancing meant that the Persians would have to liquidate the 1,400 remaining Greeks. A hoplite phalanx would be able to block the narrow pass easily, while eradicating the chance of a flank from cavalry. In Thermopylae, the phalanx would have been very difficult to assault for the more lightly armed and armored Persian infantry. The fall of King Leonidas is attributed to the miscreant Ephialtes, who defected to the Persians and showed them a goat path through the mountains, effectively sealing the King's fate. The 1,400 fought and fought until Leonidas fell, at which they surrounded and defended his body to the last breath on the
Kolonos hill. It is believed that both of Xerxes' brothers were killed in the melee.
Kolonos hill. It is believed that both of Xerxes' brothers were killed in the melee.