Thermopylae was the only pass by which an enemy could penetrate from northern into southern Greece; whence its great importance in Grecian history. It is especially celebrated on account of the heroic defence of Leonidas and the 300 Spartans against the mighty host of Xerxes in B.C. 480; and they only fell through the Persians having discovered a path over the mountains, and thus being enabled to attack the Greeks in the rear. This mountain path commenced from the neighbourhood of Trachis, ascended the gorge of the river Asopus and the hill called Anopaea, then crossed the crest of Oeta, and descended in the rear of Thermopylae near the town of Alpeni ( Herod.vii. 207-228; Pausan. iv. 35, 9; x. 19-22). See Schliemann, Untersuch. d. Thermopylen (1883); and the article Xerxes. (Harpers Dictionary of Classical Antiquities, 1898)
(Thermopulai), or simply Pylae (Pulai). "The Hot Gates," or "The Gates." A celebrated pass leading from Thessaly into Locris. It lay between Mount Oeta and an inaccessible morass, forming the edge of the Malic Gulf. At one end of the pass, close to Anthela, the mountain approaches so close to the morass as to leave room for only a single carriage between; this narrow entrance formed the western gate of Thermopylae. About a mile to the east the mountain again approached close to the sea, near the Locrian town of Alpeni, thus forming the eastern gate of Thermopylae. The space between these two gates was wider and more open, and was distinguished by its abundant flow of hot springs, which were sacred to Heracles: hence the name of the place.