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
Defeat of Regulus
When spring came (499), the state of affairs had so changed, that now the Carthaginians were the first to take the field and to offer battle to the Romans. It was natural that they should do so, for everything depended on their getting quit of the army of Regulus, before reinforcements could arrive from Italy.
The same reason should have led the Romans to desire delay; but, relying on their invincibleness in the open field, they at once accepted battle notwithstanding their inferiority of strength--for, although the numbers of the infantry on both sides were nearly the same, their 4000 cavalry and 100 elephants gave to the Carthaginians a decided superiority--and notwithstanding the unfavourable nature of the ground, the Carthaginians having taken up their position in a broad plain presumably not far from Tunes. Xanthippus, who on this day commanded the Carthaginians, first threw his cavalry on that of the enemy, which was stationed, as usual, on the two flanks of the line of battle; the few squadrons of the Romans were scattered like dust in a moment before the masses of the enemy's horse, and the Roman infantry found itself outflanked by them and surrounded.
The legions, unshaken by their apparent danger, advanced to attack the enemy's line; and, although the row of elephants placed as a protection in front of it checked the right wing and centre of the Romans, the left wing at any rate, marching past the elephants, engaged the mercenary infantry on the right of the enemy, and overthrew them completely. But this very success broke up the Roman ranks.
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Reference address : https://www.ellopos.net/elpenor/rome/3-02-war-rome-carthage-sicily.asp?pg=34