Titus Livius (Livy), The History of Rome, Book 36
Cyrus Evans, Ed.

16. With a very inferior portion of spirit, Antiochus now pitched his camp within the enclosures of this pass, the difficulties of which he increased by raising fortifications; [2] and when he had completely strengthened every part with a double rampart and trench, and, wherever it seemed requisite, with a wall formed of the stones which lay scattered about in abundance, [3??] being very confident that the Roman army would never attempt to force a passage there, he sent away one half of the four thousand Aetolians, the number that had joined him, to garrison Heraclea, which stood opposite the entrance of the defile, and the other half to Hypata; [4] for he concluded, that the consul would undoubtedly attack Heraclea, and he received accounts from many hands, that all the districts round Hypata were being laid waste. [5] The consul, after ravaging the lands of Hypata first, and then those of Heraclea, in both which places the Aetolian detachments proved useless, encamped opposite to the king, in the very entrance of the pass, near the warm springs; both parties of the Aetolians shutting themselves up in Heraclea. [6] Antiochus, who, before he saw the enemy, thought every spot perfectly well fortified, and secured by guards, now began to apprehend, that the Romans might discover some paths among the hills above, through which they could make their way; [7] for he had heard that the Lacedaemonians formerly had been surrounded in that manner by the Persians, and Philip, lately, by the Romans themselves. [8] He therefore despatched a messenger to the Aetolians at Heraclea, desiring them to afford him so [p. 1626]much assistance, at least in the war, as to seize and secure the tops of the hills, so that the Romans might not be able to pass them at any part. [9] When this message was received, a dissension arose among the Aetolians: some insisted that they ought to obey the king's orders, and go; others, that they ought to lie still at Heraclea, and wait the issue, whatever it might be; [10] for if the king should be defeated by the consul, their forces would be fresh, and in readiness to carry succour to their own states in the neighbourhood; and if he were victorious, they could pursue the Romans, while scattered in their flight. [11] Each party not only adhered positively to its own plan, but even carried it into execution; two thousand lay still at Heraclea; and two thousand, divided into three parties, took possession of the summits called Callidromus, Rhoduntia, and Tichiuns.