Titus Livius (Livy), The History of Rome, Book 31
Evan T. Sage, Ph.D. Professor of Latin and Head of the Department of Classics in the University of Pittsburgh, Ed.

37. The consul sent the cavalry to aid the harassed in any way they could, and himself led out the legions from the camp and forming a hollow square marched towards the enemy. [2] Some of the cavalry wandered aimlessly about the country, misled by the shouts that rose from this place and that, others met the enemy face to face. [3] The battle began in several places at once. The royal guard put up the stiffest fight, for by reason of the number of infantry and cavalry it was practically a regular battle and most of the Romans encountered them, since they blocked the central road. [4] In this too the Macedonians had the advantage, because the king himself was there to urge them on, and the Cretan auxiliaries dealt many unexpected wounds, fighting in close array and according to plan against men who were scattered and not in formation. [5] But if they had observed discretion in the pursuit, it would have meant not only success in the present engagement, but final victory in the war as well; [6] as it was, in their greed for slaughter, following too incautiously, they met the Roman cohorts advancing under command of the tribunes, and the fleeing cavalry, as soon as they [7] saw the standards of their friends, faced about and attacked the disordered enemy, and in a moment, the tide of battle turning, the pursuers became the pursued. [8] Many were struck down in hand-to-hand fight, many killed in flight; and they died not by the sword alone, but some of them were swallowed up, horses and all, when they became entangled in the swamps. Even the king was in danger; for, thrown headlong to the ground when [p. 111]his wounded horse fell, he narrowly escaped being¹ trampled to death. [9] A trooper saved him, who quickly leaped down and lifted the terrified king to the back of his own horse; [10] he himself, since on foot he could not equal the speed of the fleeing cavalry, perished, struck down by the cavalry who rushed up at the fall of the king. The king, riding about the marshes over roads and blind paths in full flight, came at length to his camp, when nearly all had given up hope of his safe return. [11] Two hundred of the Macedonian cavalry fell in this battle, and about one hundred were captured; [12] about eighty horses, with their trappings, some spoils of weapons being also recovered among the booty, were driven off.