Titus Livius (Livy), The History of Rome, Book 35
Cyrus Evans, Ed.

5. The battle began about the second hour. The left brigade of the allies, and the Extraordinaries, fought in the first line, and were commanded by two lieutenant-generals of consular dignity, Marcus Marcellus and Tiberius Sempronius, who had been consul the year before. [2] The present consul was sometimes employed in the front of the line, sometimes in keeping back the legions in reserve, that they might not, through eagerness for fighting, come up to the attack until the signal was given. [3] He ordered the two Minucii, Quintus and Publius, military tribunes, to lead off the cavalry of [p. 1557]the legions into open ground, at some distance from the line; and "when he should give them the signal, to charge the enemy through the clear space. [4] While he was thus employed, a message came from Tiberius Sempronius Longus, that the Extraordinaries could not support the onset of the Gauls; that great numbers had already fallen; and that partly through weariness, partly through fear, the ardour of the survivors was much abated. [5] He recommended it therefore to the consul, if he thought proper, to send up one or other of the two legions, before the army suffered disgrace. [6] The second legion was accordingly sent, and the Extraordinaries were ordered to retire. By the legion coming up, with its men fresh, and the ranks complete in their numbers, the fight was renewed with vigour. [7] The left wing was withdrawn out of the action, and the right took its place in the van. The intense heat of the sun discomposed the Gauls, whose bodies were very ill qualified to endure it: nevertheless, keeping their ranks close, and leaning sometimes on each other, sometimes on their bucklers, they withstood the attack of the Romans; [8] which, when the consul observed, in order to break their ranks, he ordered Caius Livius Salinator, commander of the allied cavalry, to charge them at full speed, and the legionary cavalry to remain in reserve. [9] This tempest of cavalry first confused and disordered, and at length entirely broke the line of the Gauls; yet it did not make them fly. [10] That was prevented by their officers, who, when they quitted their posts, struck them on the back with their spears, and compelled them to return to their ranks: but the allied cavalry, riding in among them, did not suffer them to recover their order. [11] The consul exhorted his soldiers to “continue their efforts a little longer, for victory was within their reach; to press the enemy, while they saw them disordered and dismayed; for, if they were suffered to recover their ranks, they would enter on a fresh battle with doubtful success.” [12] He ordered the standard-bearers to advance with the standards, and then, all exerting themselves at once, they at length forced the enemy to give way. As soon as they turned their backs, and fled precipitately on every side, the legionary cavalry was sent in pursuit of them. [13] On that day, fourteen thousand of the Boians were slain; one thousand and ninety-two taken —as were seven hundred and twenty-one horsemen, and three of their commanders, with [p. 1558]two hundred and twelve military standards, and sixty-three chariots. [14] Nor did the Romans gain the victory without loss of blood: of themselves, or their allies, were lost above five thousand men, twenty-three centurions, four praefects of the allies, and two military tribunes of the second legion, Marcus Genucius and Marcus Marcius.