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
These were Segesta and Halicyae, which were the first towns of Carthaginian Sicily that joined the Roman alliance; Centuripa, an inland town in the east of the island, which was destined to keep a watch over the Syracusan territory in its neighbourhood;(9) Halaesa on the northern coast, which was the first of the free Greek towns to join the Romans, and above all Panormus, hitherto the capital of Carthaginian, and now destined to become that of Roman, Sicily.
9. This is shown at once by a glance at the map, and also by the remarkable exceptional provision which allowed the Centuripans to buy to any part of Sicily. They needed, as Roman spies, the utmost freedom of movement We may add that Centuripa appears to have been among the first cities that went over to Rome (Diodorus, l. xxiii. p. 501).
The Romans thus applied to Sicily the ancient principle of their policy, that of subdividing the dependent communities into carefully graduated classes with different privileges; but, on the average, the Sardinian and Sicilian communities were not in the position of allies but in the manifest relation of tributary subjection.
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Reference address : https://www.ellopos.net/elpenor/rome/3-03-extension-italy.asp?pg=15