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
War in Sicily - Siege of Syracuse
First of all the war in Sicily came to an end. It had formed no part of Hannibal's original plan to excite a war on the island; but partly through accident, chiefly through the boyish vanity of the imprudent Hieronymus, a land war had broken out there, which--doubtless because Hannibal had not planned it--the Carthaginian council look up with especial zeal. After Hieronymus was killed at the close of 539, it seemed more than doubtful whether the citizens would persevere in the policy which he had pursued.
If any city had reason to adhere to Rome, that city was Syracuse; for the victory of the Carthaginians over the Romans could not but give to the former, at any rate, the sovereignty of all Sicily, and no one could seriously believe that the promises made by Carthage to the Syracusans would be really kept. Partly induced by this consideration, partly terrified by the threatening preparations of the Romans--who made every effort to bring once more under their complete control that important island, the bridge between Italy and Africa, and now for the campaign of 540 sent their best general, Marcus Marcellus, to Sicily--the Syracusan citizens showed a disposition to obtain oblivion of the past by a timely return to the Roman alliance.
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Reference address : https://www.ellopos.net/elpenor/rome/3-06-war-hannibal-cannae-zama.asp?pg=14