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
Fall of the Sicilian Kingdom-- Recommencement of the Italian War
The fatal embarkation took place towards the end of 478. On the voyage the new Syracusan fleet had to sustain a sharp engagement with that of Carthage, in which it lost a considerable number of vessels. The departure of the king and the accounts of this first misfortune sufficed for the fall of the Sicilian kingdom.
On the arrival of the news all the cities refused to the absent king money and troops; and the brilliant state collapsed even more rapidly than it had arisen, partly because the king had himself undermined in the hearts of his subjects the loyalty and affection on which every commonwealth depends, partly because the people lacked the devotedness to renounce freedom for perhaps but a short term in order to save their nationality.
Thus the enterprise of Pyrrhus was wrecked, and the plan of his life was ruined irretrievably; he was thenceforth an adventurer, who felt that he had been great and was so no longer, and who now waged war no longer as a means to an end, but in order to drown thought amidst the reckless excitement of the game and to find, if possible, in the tumult of battle a soldier's death.
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Reference address : https://www.ellopos.net/elpenor/rome/2-07-pyrrhus-rome-italy.asp?pg=47