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
The immediate result of the long and obstinate conflicts between them and their equally powerful and infamous antagonist, Dionysius of Syracuse (348-389), was the annihilation or weakening of the intervening Sicilian states--a result which both parties had an interest in accomplishing--and the division of the island between the Syracusans and Carthaginians.
The most flourishing cities in the island--Selinus, Himera, Agrigentum, Gela, and Messana--were utterly destroyed by the Carthaginians in the course of these unhappy conflicts: and Dionysius was not displeased to see Hellenism destroyed or suppressed there, so that, leaning for support on foreign mercenaries enlisted from Italy, Gaul and Spain, he might rule in greater security over provinces which lay desolate or which were occupied by military colonies.
The peace, which was concluded after the victory of the Carthaginian general Mago at Kronion (371), and which subjected to the Carthaginians the Greek cities of Thermae (the ancient Himera), Segesta, Heraclea Minoa, Selinus, and a part of the territory of Agrigentum as far as the Halycus, was regarded by the two powers contending for the possession of the island as only a temporary accommodation; on both sides the rivals were ever renewing their attempts to dispossess each other.
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Reference address : https://www.ellopos.net/elpenor/rome/3-01-carthage.asp?pg=23