Titus Livius (Livy), The History of Rome, Book 30
Frank Gardener Moore, Professor Emeritus in Columbia University, Ed.

34. On both sides the Punic battle-line had been stripped of its cavalry when the infantry clashed, now no longer matched either in their hopes or in their strength. In addition there were what seem small things to mention, but at the same time were highly important in the battle: a harmony in the shouting of the Romans, which consequently was greater in volume and more terrifying; [2] on the other side discordant voices, as was natural from many nations with a confusion of tongues; for the Romans a battle of little movement, as they pressed on into the [p. 495]enemy by their own weight and that of their arms; on¹ the other side repeated charges at high speed but with less power. [3] Consequently by the first attack the Romans at once dislodged the enemy's line. [4] Then beating them back with their shoulders and the bosses of their shields,² being now in close contact with men forced from their position, they made considerable progress, as no one offered any resistance, while as soon as they saw that the enemy's line had given way, even the rear line pressed upon the first, a circumstance which of itself gave them great force in repulsing the enemy. [5] Among the enemy so far was their second line, the Africans and Carthaginians, from supporting the auxiliaries as they gave way, that on the contrary they even drew back for fear the enemy, by slaying the men of the first line if these stoutly resisted, should reach themselves. [6] Accordingly the auxiliaries suddenly retreated and facing their own men, some found refuge in the second line, others, having been refused aid shortly before, and also admission now to the ranks, slashed at those who would not make place for them. [7] And by this time there were almost two battles in one, since the Carthaginians were forced to engage with the enemy and at the same time with their own men. [8] Nevertheless even so they did not admit the panic-stricken, angry men into the line, but closing up their ranks, they forced them out upon the wings and into the empty plain on this side and that outside of the battle, in order not to contaminate their own line, still intact and fresh, with soldiers alarmed by the flight and their wounds.

[9] [p. 497] But such heaps of bodies and arms had covered the³ place where the auxiliaries had stood shortly before that to make their way across was almost more difficult than it had been through the dense mass of the enemy. [10] Accordingly the men of the front line, the hastati, pursuing the enemy wherever they could over heaps of bodies and arms and through pools of blood, broke up both their own maniples and their ranks. [11] The maniples of the principes also began to waver, as they saw the unsteady line in front of them. When Scipio saw this he ordered the recall to be sounded at once for the hastati, and after withdrawing the wounded to the rear line, he led the principes and triarii to the wings, in order that the centre, composed of hastati, might be safer and steadier. [12] Thus began an entirely new battle.⁴ For they had reached the real enemy,⁵ their equals in the character of their weapons and their experience in war and the celebrity of their deeds and the greatness whether of their hopes or of [13] their danger. But the Roman was superior both in numbers and in spirit, because he had already routed the cavalry, had already routed the elephants, and was already fighting against the second line, having repulsed the first.