Thermopylae was a famous pass (its name mean literally 'the hot gates') leading from Thessaly into Locris, and the only road by which an invading army can penetrate from northern into southern Greece. It lies south of the present course of the river Sperchius, between Mount Oeta and what, in ancient times, was an impassable morass bordering on the Maliac Gulf. In the pass are several hot springs, from which Thermopylae probably received the first part of its name. Thermopylae is best known as the scene of the heroic death of Leonidas and his 300 spartans in their attempt to stem the tide of Persian invasion (480 BC). Again, in 279 BC, Brennus, at the head of a Gallic army, succeeded, through the same treachery that had secured a victory to Xerxes, in forcing the united Greeks to withdraw from the pass.