Thermopylae (thərmŏp´Ĭlē) [Gr.,=hot gates, from hot mineral springs nearby], pass, E central Greece, SE of Lamía, between the cliffs of Mt. Oeta and the Malic Gulf. Silt accumulation has gradually widened the once-narrow pass. In ancient times it was used as an entrance into Greece from the north. There in 480 BC, Leonidas with his Spartans and their allies lost a heroic battle to the Persians under Xerxes I (see Persian Wars). At the pass in 279 BC, the Greeks held back the Gauls under Brennus, who ultimately broke through, and, in 191 BC, Antiochus III of Syria was defeated there by the Romans.