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
It was evident, however, that with the possession of Lilybaeum and the departure of the king the position of the Carthaginians in the island would be nearly the same as it had been before the landing of Pyrrhus; the Greek cities if left to themselves were powerless, and the lost territory would be easily regained. So Pyrrhus rejected the doubly perfidious proposal, and proceeded to build for himself a war fleet.
Mere ignorance and shortsightedness in after times censured this step; but it was really as necessary as it was, with the resources of the island, easy of accomplishment. Apart from the consideration that the master of Ambracia, Tarentum, and Syracuse could not dispense with a naval force, he needed a fleet to conquer Lilybaeum, to protect Tarentum, and to attack Carthage at home as Agathocles, Regulus, and Scipio did before or afterwards so successfully.
Pyrrhus never was so near to the attainment of his aim as in the summer of 478, when he saw Carthage humbled before him, commanded Sicily, and retained a firm footing in Italy by the possession of Tarentum, and when the newly-created fleet, which was to connect, to secure, and to augment these successes, lay ready for sea in the harbour of Syracuse.
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Reference address : https://www.ellopos.net/elpenor/rome/2-07-pyrrhus-rome-italy.asp?pg=44