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
Relation of the Latins to the Umbro-Samnites
Among the languages of the Italian stock, again, the Latin stands in marked contrast with the Umbro-Samnite dialects. It is true that of these only two, the Umbrian and the Samnite or Oscan, are in some degree known to us, and these even in a manner extremely defective and uncertain. Of the rest some, such as the Marsian and the Volscian, have reached us in fragments too scanty to enable us to form any conception of their individual peculiarities or to classify the varieties of dialect themselves with certainty and precision, while others, like the Sabine, have, with the exception of a few traces preserved as dialectic peculiarities in provincial Latin, completely disappeared. A conjoint view, however, of the facts of language and of history leaves no doubt that all these dialects belonged to the Umbro-Samnite branch of the great Italian stock, and that this branch, although much more closely related to Latin than to Greek, was very decidedly distinct from the Latin.
In the pronoun and other cases frequently the Samnite and Umbrian used -p where the Roman used -q, as -pis- for -quis-; just as languages otherwise closely related are found to differ; for instance, -p is peculiar to the Celtic in Brittany and Wales, -k to the Gaelic and Erse. Among the vowel sounds the diphthongs in Latin, and in the northern dialects generally, appear very much destroyed, whereas in the southern Italian dialects they have suffered little; and connected with this is the fact, that in composition the Roman weakens the radical vowel otherwise so strictly preserved,--a modification which does not take place in the kindred group of languages. The genitive of words in -a is in this group as among the Greeks -as, among the Romans in the matured language -ae; that of words in -us is in the Samnite -eis, in the Umbrian -es, among the Romans -ei; the locative disappeared more and more from the language of the latter, while it continued in full use in the other Italian dialects; the dative plural in -bus is extant only in Latin. The Umbro-Samnite infinitive in -um is foreign to the Romans; while the Osco-Umbrian future formed from the root -es after the Greek fashion (-her-est- like --leg-so--) has almost, perhaps altogether, disappeared in Latin, and its place is supplied by the optative of the simple verb or by analogous formations from -fuo-(-amabo-). In many of these instances, however--in the forms of the cases, for example--the differences only exist in the two languages when fully formed, while at the outset they coincide.
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Reference address : https://www.ellopos.net/elpenor/rome/1-02-earliest-migrations-italy.asp?pg=9