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
Thus their transmarine possessions were not merely placed on the footing of land held by subjects, but were destined to remain on that footing in all time to come; whereas the official field recently marked off by law for the consuls, or, which is the same thing, the continental territory of the Romans, was to become a new and more extended Italy, which should reach from the Alps to the Ionian sea.
In the first instance, indeed, this essentially geographical conception of Italy was not altogether coincident with the political conception of the Italian confederacy; it was partly wider, partly narrower. But even now the Romans regarded the whole space up to the boundary of the Alps as -Italia-, that is, as the present or future domain of the -togati- and, just as was and still is the case in North America, the boundary was provisionally marked off in a geographical sense, that the field might be gradually occupied in a political sense also with the advance of colonization.(10)
10. This distinction between Italy as the Roman mainland or consular sphere on the one hand, and the transmarine territory or praetorial sphere on the other, already appears variously applied in the sixth century. The ritual rule, that certain priests should not leave Rome (Val. Max. i. i, 2), was explained to mean, that they were not allowed to cross the sea (Liv. Ep. 19, xxxvii. 51; Tac. Ann. iii. 58, 71; Cic. Phil. xi. 8, 18; comp. Liv. xxviii. 38, 44, Ep. 59). To this head still more definitely belongs the interpretation which was proposed in 544 to be put upon the old rule, that the consul might nominate the dictator only on "Roman ground": viz. that "Roman ground" comprehended all Italy (Liv. xxvii. 5).
The erection of the Celtic land between the Alps and Apennines into a special province, different from that of the consuls and subject to a separate Standing chief magistrate, was the work of Sulla. Of course no one will Urge as an objection to this view, that already in the sixth century Gallia or Ariminum is very often designated as the "official district" (-provincia-), usually of one of the consuls. -Provincia-, as is well known, was in the older language not--what alone it denoted subsequently--a definite space assigned as a district to a standing chief magistrate, but the department of duty fixed for the individual consul, in the first instance by agreement with his colleague, under concurrence of the senate; and in this sense frequently individual regions in northern Italy, or even North Italy generally, were assigned to individual consuls as -provincia-.
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Reference address : https://www.ellopos.net/elpenor/rome/3-03-extension-italy.asp?pg=17