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
Maritime Supremacy - Rivalry with Syracuse
All these settlements and possessions were important enough in themselves; but they were of still greater moment, inasmuch as they became the pillars of the Carthaginian maritime supremacy. By their possession of the south of Spain, of the Baleares, of Sardinia, of western Sicily and Melita, and by their prevention of Greek colonies on the east coast of Spain, in Corsica, and in the region of the Syrtes, the masters of the north coast of Africa rendered their sea a closed one, and monopolized the western straits.
In the Tyrrhene and Gallic seas alone the Phoenicians were obliged to admit the rivalry of other nations. This state of things might perhaps be endured, so long as the Etruscans and the Greeks served to counterbalance each other in these waters; with the former, as the less dangerous rivals, Carthage even entered into an alliance against the Greeks. But when, on the fall of the Etruscan power--a fall which, as is usually the case in such forced alliances, Carthage had hardly exerted all her power to avert--and after the miscarriage of the great projects of Alcibiades, Syracuse stood forth as indisputably the first Greek naval power, not only did the rulers of Syracuse naturally begin to aspire to dominion over Sicily and lower Italy and at the same time over the Tyrrhene and Adriatic seas, but the Carthaginians also were compelled to adopt a more energetic policy.
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Reference address : http://www.ellopos.net/elpenor/rome/3-01-carthage.asp?pg=22