Plutarch, Aemilius Paulus
Bernadotte Perrin, Ed.

18. Towards evening, Aemilius himself, as some say, devised a scheme for making the enemy begin the attack, and the Romans, pursuing a horse which they had driven forth without a bridle, came into collision with them, and the pursuit of this horse brought on a battle; others say that Thracians, under the command of Alexander, set upon Roman beasts of burden that were bringing in forage, and that against these a sharp sally was made by seven hundred Ligurians, whereupon reinforcements were sent to either party, and thus the engagement became general. [2] So then Aemilius, like a pilot, judging from the surging commotion in the armies the greatness of the coming storm, came forth from his tent and went along in front of his legionary troops encouraging them, and Nasica, after riding out to the skirmishers, saw that the whole force of the enemy was all but at close quarters.

[3] First the Thracians advanced, whose appearance, Nasica says, was most terrible,—men of lofty stature, clad in tunics which showed black beneath the white and gleaming armour of their shields and greaves, and tossing high on their right shoulders battle-axes with heavy iron heads. Next to the Thracians, the mercenaries advanced to the attack; their equipment was of every variety, and Paeonians were mingled with them. Next to these came a third division, picked men, the flower of the Macedonians themselves for youthful strength and valour, gleaming with gilded armour and fresh scarlet coats. [4] As these took their places in the line, they were illumined by the phalanx-lines of the Bronze-shields which issued from the camp behind them and filled the plain with the gleam of iron and the glitter of bronze, the hills, too, with the tumultuous shouts of their cheering. And with such boldness and swiftness did they advance that the first to be slain fell only two furlongs from the Roman camp.