Titus Livius (Livy), The History of Rome, Book 28
Cyrus Evans, Ed.

13. When Scipio received an account of the collection of so large an army, he felt convinced that he would not be a match for so great a multitude with the Roman legions only, without making a show at least of the auxiliary troops of the barbarians; [2] at the same time that he did not think it right that they should form so large a portion of his force as to occasion important consequences if they should change sides, which had brought ruin upon his father and his uncle. [3] Therefore, sending forward Silanus to Colca, who was sovereign of twenty-eight towns, to receive from him the infantry and cavalry, which he promised to enlist during the [p. 1179]winter, he himself set out from Tarraco; [4] and collecting small bodies of auxiliaries from his allies, who lay near his road as he proceeded, he came to Castulo. [5] To this place Silanus led the auxiliaries, consisting of three thousand infantry and five hundred horse. Thence he advanced to the city of Baecula, with his entire army of countrymen and allies, foot and horse, amounting to forty-five thousand. [6] Mago and Masinissa attacked them with the whole body of their cavalry while forming their camp, and would have dispersed those engaged in the works, had not a party of horse, concealed by Scipio behind an eminence conveniently situated for the purpose, unexpectedly charged them when rushing on to [7??] the attack, and, ere the battle was well begun, routed all the most forward, both those who had advanced nearest the rampart, and those who were foremost in charging the very workmen. With the rest of the troops who came up with their standards, and in order of march, the contest lasted longer, and was for a considerable time doubtful. [8] But when first the light cohorts from the outposts, and then the troops withdrawn from the works and ordered to take arms, came up, being more numerous than those which had been engaged, and fresh while they were fatigued, and now a large body of armed troops rushed from the camp to the battle, the Carthaginians and Numidians at once turned their backs. [9] At first they moved off in troops without breaking their ranks, through fear or precipitation; but afterwards, when the Romans pressed furiously upon their rear, and they were unable to bear the violence of their attack, then at length, utterly regardless of order, they fled precipitately in every direction, as suited each man's convenience. [10] And although, in consequence of this battle, the spirits of the Romans were considerably raised, and those of the enemy depressed, yet, for several days following, the horsemen and light-armed troops never ceased from skirmishes.