Thermopylae, Or Simply Pylae (From θερμός, hot, and πύλη, gate), a defile between Thessaly and Locris, in antiquity the only passage for an enemy from northern into central Greece, situated between Mt. (Eta and an inaccessible morass forming the edge of the Maliac' gulf, and containing several hot springs. There was a road wide enough only for a single wheel track, which formed the western gate. About a mile to the eastward Mt. Oeta again approached the sea in a similar manner, and the passage there formed the eastern gate. The space between these two gates was wider, and many years before Leonidas occupied the pass, the Phocians had so conducted the warm springs over the ground as to render the pass impracticable. They had also built a wall near the western gate to prevent the incursions of the Thessalians, which was in ruins when the Spartans came. This pass is celebrated for its defence against the army of Xerxes by the Greeks under the Spartan king Leonidas, in 480 B. C. His forces numbered probably about 7,000; but when during the battle he learned that one Ephialtes, a Thcssalian, had betrayed to the Persians a circuitous path over the mountains leading to their rear, he dismissed all but his chosen band of 300 Spartans, with a number of helots, about 700 Thespians who volunteered to share his fate, and apparently 400 Thebans. This small host sallied out and fought till Leonidas and all the Spartans and Thespians were killed.

The fate of the Thebans is uncertain; according to some they surrendered to the Persians. One Spartan, Aris-todemus, who was prevented by illness from partaking in the combat, returned home, and was received with scorn, but in the following year retrieved his honor by a heroic death at Theroigne De mericourt Platsea. Many other battles took place at Thermopylae in later times. - The pass is now of little importance as a strategic point. Nature has widened it into a swampy plain from the alluvial deposit of the Spercheus and the retreat of the Maliac gulf. At the S. end of the pass is a mound, supposed to be that to which the Spartans finally retreated and on which they were slain. In a small plain is the Polyandrium, one of the sepulchral monuments of the Greeks who fell at Thermopylae, and a few miles beyond are the remains of the wall mentioned above, which can be traced from the Maliac gulf to the gulf of Corinth.