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
But even the statesman, with whom political morality was no mere phrase, might ask in reply, how Roman burgesses, who had broken their military oath and treacherously murdered the allies of Rome, could be placed on a level with foreigners who had committed an outrage on foreigners, where no one had constituted the Romans judges of the one or avengers of the other? Had the question been only whether the Syracusans or Mamertines should rule in Messana, Rome might certainly have acquiesced in the rule of either.
Rome was striving for the possession of Italy, as Carthage for that of Sicily; the designs of the two powers scarcely then went further. But that very circumstance formed a reason why each desired to have and retain on its frontier an intermediate power--the Carthaginians for instance reckoning in this way on Tarentum, the Romans on Syracuse and Messana--and why, if that course was impossible, each preferred to see these adjacent places given over to itself rather than to the other great power.
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Reference address : https://www.ellopos.net/elpenor/rome/3-02-war-rome-carthage-sicily.asp?pg=8