11 August 480 BC, King Leonidas is killed in the battle of Thermopylae, where 300 Spartans fought bravely against thousands of Persians.

Battle of Thermopylae, (480 bce), battle in central Greece at the mountain pᴀss of Thermopylae during the Persian Wars. The Greek forces, mostly Spartan, were led by Leonidas. After three days of holding their own against the Persian king Xerxes I and his vast southward-advancing army, the Greeks were betrayed, and the Persians were able to outflank them. Sending the main army in retreat, Leonidas and a small contingent remained behind to resist the advance and were defeated.

The Battle of Thermopylae’s political origins can be traced back to Xerxes’ predecessor, Darius I (the Great), who sent heralds to Greek cities in 491 bce in the hopes of persuading them to accept Persian authority. This offended the proud Greeks greatly; the Athenians went so far as to toss the Persian heralds into a pit, while the Spartans followed suit and tossed them into a well. In 480 bce Xerxes invaded Greece as a continuation of Darius’s original plan. He began the same way his predecessor had: he sent heralds to Greek cities—but he skipped over Athens and Sparta because of their previous responses. Many Greek city-states either joined Xerxes or remained neutral, while Athens and Sparta led the resistance with a number of other city-states behind them. Before invading, Xerxes implored the Spartan king Leonidas to surrender his arms. Leonidas famously replied, “Come and take them” (“Molon labe”). Xerxes intended to do just that and thus moved toward Thermopylae.

Xerxes led a vast army overland from the Dardanelles, accompanied by a substantial fleet moving along the coast. His forces quickly seized northern Greece and began moving south. The Greek resistance tried to halt Persian progress on land at the narrow pᴀss of Thermopylae and at sea nearby in the straits of Artemisium. The Greek army was led by Leonidas, who was estimated to have had around 7,000 men. Xerxes, on the other hand, had anywhere from 70,000 to 300,000. Despite the disparity in numbers, the Greeks were able to maintain their position. Their strategy involved holding a line only a few dozen yards long between a steep hillside and the sea. This constricted the battlefield and prevented the Persians from utilizing their vast numbers. For two days the Greeks defended against Persian attacks and suffered light losses as they imposed heavy casualties on the Persian army. Only when the Greeks were betrayed did the battle take a detrimental turn for them. Ephialtes, a Greek citizen desiring reward, informed Xerxes of a path that went around Thermopylae, thus rendering the Greeks’ line useless in preventing forward advancement of the Persian army.