THERMUM, THERMUS or THERMA (τὸ Θέρμον, Plb. 5.8; τὰ Θέρμα, Strab. 10. p. 463; Plb. 5.7; Θέμος, Steph. B. s. v.: Eth. Θέρμιος : Vlokho), the chief city of Aetolia during the flourishing period of the Aetolian League, and the place where the meetings of the league were usually held and an annual festival celebrated. It possessed a celebrated temple of Apollo, in connection with which the festival was probably celebrated. It was situated in the very heart of Aetolia, N. of the lake Trichonis, and on a height of Mt. Panaetolium ( Viena). It was considered inaccessible to an army, and from the strength of its situation was regarded as a place of refuge, and, as it were, the Acropolis of all Aetolia. The road to it ran from Metapa, on the lake Trichonis, through the village of Pamphia. The city was distant 60 stadia from Metapa, and 30 from Pamphia; and from the latter place the road was very steep and dangerous, running along a narrow crest with precipices on each side. It was, however, surprised by Philip V., king of Macedonia, in his invasion of Aetolia in B.C. 218. The Aetolians, who had never imagined that Philip would have penetrated so far into their country, had deposited here all their treasures, the whole of which now fell into the hands of the king, together with a vast quantity of arms and armour. He carried off the most valuable part of the spoil, and burnt all the rest, among which were more than 15,000 suits of armour. Not content with this, he set fire to the sacred buildings, to retaliate for the destruction of Dium and Dodona. He also defaced all the works of art, and threw down all the statues, which were not less than 2000 in number, only sparing those of the Gods. (Plb. 5.6—9, 13.) A few years afterwards, when the Aetolians had sided with the Romans, Philip again surprised Thermus (about B.C. 206), when he destroyed everything which had escaped his ravages in his first attack. (Plb. 11.4.) We have no further details of the history of Thermum. Polybius alludes, in one or two other passages (18.31, 28.4), to the meetings of the league held there. In the former of these passages Livy (Liv. 33.35) has misunderstood the words τὴν τῶν Θερμικῶν σύνοδονto mean the assembly held at Thermopylae.
Polybius's account of Philip's first invasion of Aetolia, which resulted in the capture of Thermum, supplies us with the chief information respecting the towns in the central plain of Aetolia. Philip set out from Limnaea, on the south-eastern corner of the Ambraciot gulf, crossed the Achelous between Stratus and Conope, and marched with all speed towards Thermum, leaving on his left Stratus, Agrinium, and Thestienses (Θεστιεῖς), and on his right Conope, Lysimachia, Trichonium, and Phoeteum. He thus arrived at Metapa, on the lake Trichonis, and from thence marched to Thermus by the road already mentioned, passing by Pamphia in his way. He returned by the same road as far as Metapa, but from the latter place he marched in one day to a place called Acrae, where he encamped, and on the next day to Conope. After remaining a day at Conope, he marched up the Achelous, and crossed it near Stratus.
The remains of the walls of Thermum show that the city was about 2 1/2 miles in circumference. It was in the form of a triangle on the slope of a pyramidal hill, bordered on either side by a torrent flowing in a deep ravine. The only remains of a public edifice within the walls consist of a square, pyramidal, shapeless mass of stones. (Leake, Northern Greece, vol. 1. p. 126, &c.)