Titus Livius (Livy), The History of Rome, Book 22
D. Spillan, A.M., M.D., Cyrus Evans, Ed.

47. The shout being raised, the auxiliaries charged, and the battle commenced in the first place with the light-armed troops: then the left wing, consisting of the Gallic and Spanish cavalry, engages with the Roman right wing, by no means in the manner of a cavalry battle; [2] for they were obliged to engage front to front; for as on one side the river, on the other the line of infantry hemmed them in, there was no space left at their flanks for evolution, but both parties were compelled to press directly forward. [3] At length the horses standing still, and being crowded together, man grappling with man, dragged him from his horse. The contest now came to be carried on principally on foot. The battle, however, was more violent than lasting; and the Roman cavalry being repulsed, turn their backs. [4] About the conclusion of the contest between the cavalry, the battle between the infantry commenced. At first the Gauls and Spaniards preserved their ranks unbroken, not inferior in strength or courage: [5] but at length the Romans, after long and repeated efforts, drove in with their even front and closely compacted line, that part of the enemy's line in the form of a wedge, which projected beyond the rest, which was too thin, and therefore deficient in strength. [6] These men, thus driven back and hastily retreating, they closely pursued; and as they urged their course without interruption through this terrified band, as it fled with precipitation, were borne first upon the centre line of the enemy; and lastly, no one opposing them, they reached the African reserved troops. [7] These were posted at the two extremities of the line, where it was depressed; while the centre, where the Gauls and Spaniards were placed, projected a little. When [p. 817]the wedge thus formed being driven in, at first rendered the line level, but afterwards, by the pressure, made a curvature in the centre, the Africans, who had now formed wings on each side of them, surrounded the Romans [8??] on both sides, who incautiously rushed into the intermediate space; and presently extending their wings, enclosed the enemy on the rear also. [9] After this the Romans, who had in vain finished one battle, leaving the Gauls and Spaniards, whose rear they [10??] had slaughtered, in addition commence a fresh encounter with the Africans, not only disadvantageous, because being hemmed in they had to fight against troops who surrounded them, but also because, fatigued, they fought with those who were fresh and vigorous.