Titus Livius (Livy), The History of Rome, Book 27
Cyrus Evans, Ed.

48. First Nero arrived with the whole body of his cavalry; then Porcius came up with him, with the light infantry. [2] And while these were harassing his weary troops on every side, and charging them, and the Carthaginian, stopping his march, which resembled a flight, was desirous of encamping on an eminence, on the bank of the river, Livius came up with all his [3??] foot forces, not after the manner of troops on march, but armed and marshalled for immediate action. [4] When they had united all their forces, and the line was drawn out, Claudius took the direction of the battle in the right wing, Livius in the left; the management of the centre was given to the praetor. [5] Hasdrubal, when he saw that an engagement was inevitable, giving over the fortification of a camp, placed his elephants in the front line, before the standards; on either side these he placed in the left wing the Gauls to oppose Claudius, not so much from any confidence he reposed in them, as because he believed them to be dreaded by the enemy; [6] the right wing he took to himself against M. Livius, together with the Spaniards, in whom, as being veteran troops, he placed his greatest hopes. [7] Behind the elephants, in the centre, the Ligurians were posted; but his line was rather long than deep. The Gauls were covered by a hill, which extended in front. [8] That part of the line which was occupied by the Spaniards, engaged the left wing of the Romans, the whole of whose right wing, extending beyond the line of battle, was unengaged. The hill before them prevented their making an attack either in front or flank. [9] Between Livius and Hasdrubal a furious contest arose, and the slaughter on both sides was dreadful. [10] Here were both the generals, here the major part of the Roman horse and infantry, here the Spaniards, veteran troops, and experienced in the Roman manner of fighting, and the Ligurians, a nation inured to war. [11] The elephants were also driven to the same part, which, on the first onset, disordered the van, and had now [p. 1157]even dislodged the standards; but afterwards, the contest growing hotter, and the shout increasing, they became less submissive to their riders, and ranged to and fro between the two lines, as if not knowing to which side they belonged, like ships floating about without rudders. [12] Claudius, when he had striven in vain to advance up the hill, repeatedly calling out to his soldiers, “To what purpose then have we performed so long a march with such expedition?” [13] when he found it impossible to make his way to the enemy in that quarter, withdrawing several cohorts from the right wing, where he saw they would occupy an inactive station, rather than join in the fight, led them round the rear of the line, and, to the surprise not only of the enemy but his own party, charged their right flank; [14] and such was their rapidity, that after showing themselves on their flank, they almost immediately made an attack on their rear. Thus on all sides, in front, flank, and rear, the Spaniards and Ligurians were cut to pieces; and now the carnage had even reached the Gauls. [15] Here the least opposition was found; for a great number [16??] of them had quitted their standards, having slunk off during the night, and laid themselves down to sleep up and down the fields, while even those who were present, being tired with marching and watching, for their bodies are most intolerant of fatigue, could scarcely carry their arms upon their shoulders. [17] And now it was midday, and thirst and heat gave them over to the enemy to be killed or captured in multitudes.