Titus Livius (Livy), The History of Rome, Book 36
Evan T. Sage, PhD professor of latin and head of the department of classics in the University of Pittsburgh, Ed.

15. While this was going on Antiochus was at Chalcis, now at last perceiving that he had gained nothing from Greece except a pleasant winter at Chalcis and a shameful marriage. [2] Then he began to blame the false promises of the Aetolians and [p. 203]to censure Thoas, but Hannibal he admired as not¹ only a wise man but as little less than a prophet of all that was happening. [3] Yet, not to risk still more his rash enterprise by his own inactivity, he sent messages to Aetolia that they should assemble all their youth and meet at Lamia; and he too led there about ten thousand infantry, including replacements from those who had later arrived from Asia, and five hundred cavalry. [4] When a somewhat smaller number than ever before had-assembled there, only the chiefs, in fact, with a few clients,² and these explained that they had worked with all diligence to call out the largest possible numbers from- their cities, but had prevailed by neither [5??] influence nor persuasion nor right of command against the shirkers of military service, then, abandoned on all sides, both by his own subjects, who were tarrying in Asia, and by his allies, who were not fulfilling the promises by the hope of which they had invited him, he retired within the pass of Thermopylae.³ [6] This ridge, just as Italy is cut in two by the backbone of the Apennines, divides Greece. [7] In front of the pass of Thermopylae, facing the north, are Epirus and Perrhaebia and Magnesia and Thessaly and Phthiotic Achaea and the Malian gulf; [8] within the pass towards the south lie the larger part of Aetolia and Acarnania and Phocis with Locris and Boeotia with the island of Euboea adjoining it and, on a sort of promontory running out into the sea, the [p. 205]Attic land, and lying behind it the Peloponnesus.⁴ [9] This range, taking its course from Leucas and the sea on the west and continuing through Aetolia to the other sea on the east, has such thickets and scattered cliffs that not even individuals travelling light, not to mention armies, can easily find paths by which to cross. [10] The mountains on the extreme east they call Oeta, the highest of which is named Callidromum, in the valley of which, where it slopes down to the Malian gulf, there is a road not wider than sixty paces. This is the one military road where an army can pass if there is no resistance.⁵ [11] For that reason the place is called Pylae and by others, because there are warm springs within the pass itself, [12??] Thermopylae,⁶ and it is renowned for the death of the Lacedaemonians as they opposed the Persians, more memorable than the battle.