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
Hiero of Syracuse - War between the Syracusans and the Mammertines
It is not becoming in the historian either to excuse the perfidious crime by which the Mamertines seized their power, or to forget that the God of history does not necessarily punish the sins of the fathers to the fourth generation. He who feels it his vocation to judge the sins of others may condemn the human agents; for Sicily it might be a blessing that a warlike power, and one belonging to the island, thus began to be formed in it--a power which was already able to bring eight thousand men into the field, and which was gradually putting itself in a position to take up at the proper time and on its own resources that struggle against the foreigners, to the maintenance of which the Greeks, becoming more and more unaccustomed to arms notwithstanding their perpetual wars, were no longer equal.
In the first instance, however, things took another turn. A young Syracusan officer, who by his descent from the family of Gelo and his intimate relations of kindred with king Pyrrhus as well as by the distinction with which he had fought in the campaigns of the latter, had attracted the notice of his fellow-citizens as well as of the Syracusan soldiery--Hiero, son of Hierocles--was called by military election to command the army, which was at variance with the citizens (479-480). By his prudent administration, the nobility of his character, and the moderation of his views, he rapidly gained the hearts of the citizens of Syracuse--who had been accustomed to the most scandalous lawlessness in their despots--and of the Sicilian Greeks in general.
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Reference address : https://www.ellopos.net/elpenor/rome/3-02-war-rome-carthage-sicily.asp?pg=4