Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Hungry, weary, and wet, the Romans came on and hastened to form in order of battle, the cavalry, as usual, on the wings, the infantry in the centre. The light troops, who formed the vanguard on both sides, began the combat: but the Romans had already almost exhausted their missiles against the cavalry, and immediately gave way.
In like manner the cavalry gave way on the wings, hard pressed by the elephants in front, and outflanked right and left by the far more numerous Carthaginian horse. But the Roman infantry proved itself worthy of its name: at the beginning of the battle it fought with very decided superiority against the infantry of the enemy, and even when the repulse of the Roman horse allowed the enemy's cavalry and light-armed troops to turn their attacks against the Roman infantry, the latter, although ceasing to advance, obstinately maintained its ground.
At this stage a select Carthaginian band of 1000 infantry, and as many horsemen, under the leadership of Mago, Hannibal's youngest brother, suddenly emerged from an ambush in the rear of the Roman army, and fell upon the densely entangled masses.
The wings of the army and the rear ranks of the Roman centre were broken up and scattered by this attack, while the first division, 10,000 men strong, in compact array broke through the Carthaginian line, and made a passage for itself obliquely through the midst of the enemy, inflicting great loss on the opposing infantry and more especially on the Gallic insurgents. This brave body, pursued but feebly, thus reached Placentia.
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Reference address : https://www.ellopos.net/elpenor/rome/3-05-war-hannibal-cannae.asp?pg=8