THERMOPYLAE (Gr. θερμός, hot, and πύλη, gate), a Greek pass leading from Locris into Thessaly between Mount Oeta and the sea. (Maliac Gulf). It is chiefly famous for the heroic defence made by Leonidas, the Spartan king, with 300 Spartan soldiers against the Persian army of Xerxes advancing upon Greece in 480 (see Leonidas and authorities there quoted). Two other famous battles took place at the pass. In 279 B.C. Brennus and the Gauls were checked for several months by a Greek army under the Athenian Calippus, and in 191 Antiochus of Syria vainly attempted to hold the pass against the Romans under M'. Acilius Glabrio. In the time of Leonidas the pass was a narrow track (probably about 14 yds. wide) under the cliff. In modern times the deposits of the Spercheius have widened it to a breadth of 112 to 3 m. broad. The hot springs from which the pass derived its name still exist close to the foot of the hill. There is one large spring used as a bath and four smaller ones, and the water, which is of a bluish green colour and contains lime, salt, carbonic acid and sulphur, is said to produce good effects in cases of scrofula, sciatica and rheumatism. The accommodation for bathers is, however, quite inadequate.
For the topography see Grundy, Great Persian War, pp. 277–291,