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
Corruption of Language and Writing
Lastly it is a significant fact, that among all the Italian stocks the development of the Greek alphabet primarily consisted in a process of corruption. Thus the -mediae- disappeared in the whole of the Etruscan dialects, while the Umbrians lost -"γάμμα" and -"d", the Samnites -"d", and the Romans -"γάμμα"; and among the latter -"d" also threatened to amalgamate with -"r". In like manner among the Etruscans -"o" and -"u" early coalesced, and even among the Latins we meet with a tendency to the same corruption.
Nearly the converse occurred in the case of the sibilants; for while the Etruscan retained the three signs -"z", -"s", -"sh", and the Umbrian rejected the last but developed two new sibilants in its room, the Samnite and the Faliscan confined themselves like the Greek to -"s" and -"z", and the Roman of later times even to -"s" alone. It is plain that the more delicate distinctions of sound were duly felt by the introducers of the alphabet, men of culture and masters of two languages; but after the national writing became wholly detached from the Greek mother-alphabet, the -mediae- and their -tenues- gradually came to coincide, and the sibilants and vowels were thrown into disorder--transpositions or rather destructions of sound, of which the first in particular is entirely foreign to the Greek.
The destruction of the forms of flexion and derivation went hand in hand with this corruption of sounds. The cause of this barbarization was thus, upon the whole, simply the necessary process of corruption which is continuously eating away every language, where its progress is not stemmed by literature and reason; only in this case indications of what has elsewhere passed away without leaving a trace have been preserved in the writing of sounds.
The circumstance that this barbarizing process affected the Etruscans more strongly than any other of the Italian stocks adds to the numerous proofs of their inferior capacity for culture. The fact on the other hand that, among the Italians, the Umbrians apparently were the most affected by a similar corruption of language, the Romans less so, the southern Sabellians least of all, probably finds its explanation, at least in part, in the more lively intercourse maintained by the former with the Etruscans, and by the latter with the Greeks.
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Reference address : https://www.ellopos.net/elpenor/rome/1-14-measuring-writing.asp?pg=29