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
League between Rome and Carthage-- Third Year of the War
The immediate effect, indeed, of this union of the Italian and Sicilian Greeks under one control was a closer concert also on the part of their antagonists. Carthage and Rome now converted their old commercial treaties into an offensive and defensive league against Pyrrhus (475), the tenor of which was that, if Pyrrhus invaded Roman or Carthaginian territory, the party which was not attacked should furnish that which was assailed with a contingent on its own territory and should itself defray the expense of the auxiliary troops; that in such an event Carthage should be bound to furnish transports and to assist the Romans also with a war fleet, but the crews of that fleet should not be obliged to fight for the Romans by land; that lastly, both states should pledge themselves not to conclude a separate peace with Pyrrhus.
The object of the Romans in entering into the treaty was to render possible an attack on Tarentum and to cut off Pyrrhus from his own country, neither of which ends could be attained without the co-operation of the Punic fleet; the object of the Carthaginians was to detain the king in Italy, so that they might be able without molestation to carry into effect their designs on Syracuse.(5) It was accordingly the interest of both powers in the first instance to secure the sea between Italy and Sicily.
5. The later Romans, and the moderns following them, give a version of the league, as if the Romans had designedly avoided accepting the Carthaginian help in Italy. This would have been irrational, and the facts pronounce against it. The circumstance that Mago did not land at Ostia is to be explained not by any such foresight, but simply by the fact that Latium was not at all threatened by Pyrrhus and so did not need Carthaginian aid; and the Carthaginians certainly fought for Rome in front of Rhegium.
A powerful Carthaginian fleet of 120 sail under the admiral Mago proceeded from Ostia, whither Mago seems to have gone to conclude the treaty, to the Sicilian straits. The Mamertines, who anticipated righteous punishment for their outrage upon the Greek population of Messana in the event of Pyrrhus becoming ruler of Sicily and Italy, attached themselves closely to the Romans and Carthaginians, and secured for them the Sicilian side of the straits.
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