The Battle of Thermopylae was fought over the course of three days in 480 BC, between an alliance of the city-states of Ancient Greece and the Persian Empire under Xerxes I. Herodotus describes the heroic stand by the Spartans, who fought to their deaths against a much larger Persian force, allowing the rest of the Greek army to withdraw safely.
Three hundred Spartans led by King Leonidas, alongside a force of over a thousand Thebans, Thespians, and others, held the pass at Thermopylae against a Persian force which numbered between 70,000-300,000. The Greek force was largely destroyed, but they resisted the Persians long enough to save the rest of the Greek army. Simonides composed an epigram to commemorate the bravery of the Spartans, which was engraved on a stone at the site of the battle:
Go tell the Spartans, thou who passest by,
That here, obedient to their laws, we lie.