300 Spartans held a mountain pass for three days — until one man talked

In 480 BC, King Leonidas I of Sparta led a few thousand Greeks, including his famed 300 Spartans, to block the vast Persian army of Xerxes I at the narrow pass of Thermopylae. They held for three days until a local named Ephialtes showed the Persians a hidden path around. Leonidas sent most of his army away and made a last stand with the Spartans, dying with his men.

— Paul Cartledge, Thermopylae: The Battle That Changed the World — 2006
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