Battle of Thermopylae and Artemisium began in 480 BCE

The Battle of Thermopylae and the simultaneous naval Battle of Artemisium began in 480 BCE during the Greco-Persian Wars. Persian King Xerxes I led a massive invasion force, estimated between 100,000 and 250,000 soldiers, in response to Athenian interference in the Ionian Revolt and previous Persian military failures.

At the suggestion of Athenian general Themistocles, Greek forces attempted to block the Persians at both the Thermopylae pass on land and the straits of Artemisium at sea. Due to ongoing religious festivals in Greece, the Greek defense was limited to approximately 10,000 soldiers, including King Leonidas and his elite guard of 300 Spartan hoplites.

Using a defensive wall and the phalanx formation, the Greeks successfully blocked the narrow pass for two days, inflicting heavy casualties on the Persian forces. The stalemate was eventually broken when a local resident, Ephialtes, informed the Persians of a mountain path that allowed them to bypass the Greek position.