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
In its further course the alphabet experienced various fortunes in connection with the several stocks, the Etruscans on the Arno and around Capua, the Umbrians and the Samnites; frequently the mediae were entirely or partially lost, while elsewhere again new vowels and consonants were developed.
But that West-Etruscan reform of the alphabet was not merely as old as the oldest tombs found in Etruria; it was considerably older, for the syllabarium just mentioned as found probably in one of these tombs already presents the reformed alphabet in an essentially modified and modernized shape; and, as the reformed alphabet itself is relatively recent as compared with the primitive one, the mind almost fails in the effort to reach back to the time when that alphabet came to Italy.
While the Etruscans thus appear as the instruments in diffusing the alphabet in the north, east, and south of the peninsula, the Latin alphabet on the other hand was confined to Latium, and maintained its ground, upon the whole, there with but few alterations; only the letters -"γάμμα" -"κάππα" and -"ζῆτα" -"σίγμα" gradually became coincident in sound, the consequence of which was, that in each case one of the homophonous signs (-"κάππα" -"ζῆτα") disappeared from writing.
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Reference address : https://www.ellopos.net/elpenor/rome/1-14-measuring-writing.asp?pg=23