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

19. Flaccus had not met the same good fortune at Tichiuns and Rhoduntia; having failed in his attempts to approach those fastnesses. [2] The Macedonians, and others, in the king's camp, as long as, on account of the distance, they could distinguish nothing more than a body of men in motion, thought they were the Aetolians, who, on seeing the fight, were coming to their aid. [3] But when, on a nearer view, they knew the standards and arms, and thence discovered their mistake, they were all instantly seized with such a panic, that they threw down their arms and fled. [4] Both the fortifications retarded the pursuers, and the narrowness of the valley through which the troops had to pass; and, above all, the circumstance that the elephants were on the rear of the enemy. These the infantry could with difficulty pass, and the cavalry could by no means do so, their horses being so frightened, that they threw one another into greater confusion than when in battle. [5] The plundering of the camp also caused a considerable delay. [6] But, notwithstanding all this, the Romans pursued the enemy that day as far as Scarphea, killing and taking on the way great numbers both of men and horses, and also killing such of the elephants as they could not capture; and then they returned to their camp. [7] This had been attacked, during the time of the action, by the Aetolians who were occupying Heraclea as a garrison, but the enterprise, which certainly showed no want of boldness, was not attended with any success. [8] The consul, at the third watch of the following night, sent forward his cavalry in pursuit of the enemy; and, as soon as day appeared, set out at the head of the legions. [9] The king had got far before him, as he did not halt in his precipitate flight until he came to Elatia. There having collected the survivors of the battle and the retreat, he, with a very small body of half-armed men, betook himself to Chalcis. [10] The Roman cavalry did not overtake the king himself at Elatia; but they cut off a great part of his soldiers, who either halted through weariness, or wandered out of the way through mistake, as they fled without guides through unknown roads; [11] so that, out of the whole army, not one escaped except five hundred, who kept close about the king; and even of the ten thousand men, whom, on the authority of Polybius, we [p. 1630]have mentioned as brought over by the king from Asia, a very trifling number got off. [12] But what shall we say if we are to believe Valerius Antias, who records that there were in the king's army sixty thousand men, of whom forty thousand fell, and above five thousand were taken, with two hundred and thirty military standards? Of the Romans were slain in the action itself a hundred and fifty; and of the party that defended themselves against the assault of the Aetolians, not more than fifty.