As the whole battle was a hand-to-hand affair [the men using neither spears nor swords], the mercenaries at first prevailed by their courage and skill, wounding many of the Romans,
but the latter still continued to advance, relying on their admirable order and on the superiority of their arms.
The rear ranks of the Romans followed close on their comrades, cheering them on, but the Carthaginians behaved like cowards, never coming near their mercenaries nor attempting to back them up,
so that finally the barbarians gave way, and thinking that they had evidently been left in the lurch by their own side, fell upon those they encountered in their retreat and began to kill them.
This actually compelled many of the Carthaginians to die like men; for as they were being butchered by their own mercenaries they were obliged against their will to fight both against these and against the Romans,
and as when at bay they showed frantic and extraordinary courage, they killed a considerable number both of their mercenaries and of the enemy.
In this way they even threw the cohorts of the hastati into confusion, but the officers of the principes, seeing what was happening, brought up their ranks to assist,
and now the greater number of the Carthaginians and their mercenaries were cut to pieces where they stood, either by themselves or by the hastati.
Hannibal did not allow the survivors in their flight to mix with his own men but, ordering the foremost ranks to level their spears against them, prevented them from being received into his force.
They were therefore obliged to retreat towards the wings and the open ground beyond.
Walbank Commentary