Titus Livius (Livy), The History of Rome, Book 31
Cyrus Evans, Ed.

37. The consul, ordering the cavalry to carry aid to those who were in danger, in the best manner they could, drew out the legions from the camp, and led them drawn up in a square towards the enemy. [2] The cavalry, taking different ways through the fields, missed the road, being deceived by the various shouts raised in several quarters. [3] Some of them met with the enemy, and battles began in many places at once. The hottest part of the action was at the station where the king commanded; for the guard there was, in numbers both of horse and foot, almost a complete army; and, as they were posted on the middle road, the greatest number of the Romans fell in with them. [4] The Macedonians had also the advantage in this, that the king himself was present to encourage them; and the Cretan auxiliaries, fighting in good order, and in a state of preparation, against troops disordered and irregular, wounded many at a distance, where no such danger was apprehended. [5] If they had acted with prudence in the pursuit, they would have secured an advantage of great importance, not only in regard to the glory of the present contest, but to the general interest of the war; [6] but, greedy of slaughter, and following with too much eagerness, they fell in with the advanced cohorts of the Romans under the military tribunes. [7] The horsemen who were flying, as soon as they saw the ensigns of their friends, faced about against the enemy, now in disorder; so that in a moment's time the fortune of the battle was changed, those now turning their backs who had lately been the pursuers. [8] Many were slain in close fight, many in the pursuit; nor was it by the sword alone that they perished; several, being driven into morasses, were, together with their horses, swallowed up in the deep mud. [9] The king himself was in danger; for his horse falling, in consequence of a wound, threw him headlong to the ground, and he very narrowly escaped being overpowered while prostrate. [10] He owed his safety to a trooper, who instantly leaped down and mounted the affrighted king on his horse; himself, as he could not on foot keep up with the flying horsemen, was slain by the enemy, who had collected about the place where Philip fell. [11] The king, in his desperate flight, rode about among the morasses, some of which were easily passed, and others not; [p. 1380]at length, when most men despaired of his ever escaping in safety, he arrived in safety at his camp. Two hundred Macedonian horsemen perished in that action; about one hundred were taken: [12] eighty horses, richly caparisoned, were led off the field; at the same time the spoils of arms were also carried off.