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
Grievances not unfounded, but half-forgotten, once more emerged--it seemed not superfluous amidst other warlike preparations to replenish the diplomatic armoury with reasons for war, and for the coming manifesto to reserve to themselves, as was the custom of the Romans, the character of the party aggrieved. This much at least might with entire justice be affirmed, that the respective enterprises on Tarentum and Messana stood upon exactly the same footing in point of design and of pretext, and that it was simply the accident of success that made the difference. Carthage avoided an open rupture.
The ambassadors carried back to Rome the disavowal of the Carthaginian admiral who had made the attempt on Tarentum, along with the requisite false oaths: the counter-complaints, which of course were not wanting on the part of Carthage, were studiously moderate, and abstained from characterizing the meditated invasion of Sicily as a ground for war. Such, however, it was; for Carthage regarded the affairs of Sicily --just as Rome regarded those of Italy--as internal matters in which an independent power could allow no interference, and was determined to act accordingly.
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Reference address : https://www.ellopos.net/elpenor/rome/3-02-war-rome-carthage-sicily.asp?pg=12