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
The language was, if not yet stereotyped, in the course of becoming so; it was not yet indeed unthinkingly dominated by rule, but it had already become conscious of it. That this action in the department of Latin grammar derived generally its spirit and method from the Greek, and not only so, but that the Latin language was also directly rectified in accordance with Greek precedent, is shown, for example, by the treatment of the final -s, which till towards the close of this epoch had at pleasure passed sometimes as a consonant, sometimes not as one, but was treated by the new- fashioned poets throughout, as in Greek, as a consonantal termination.
This regulation of language is the proper domain of Roman classicism; in the most various ways, and for that very reason all the more significantly, the rule is inculcated and the offence against it rebuked by the coryphaei of classicism, by Cicero, by Caesar, even in the poems of Catullus; whereas the older generation expresses itself with natural keenness of feeling respecting the revolution which had affected the field of language as remorselessly as the field of politics.(5)
5. Thus Varro (De R. R. i. 2) says: -ab aeditimo, ut dicere didicimus a patribus nostris; ut corrigimur ab recenlibus urbanis, ab aedituo-.
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Reference address : https://www.ellopos.net/elpenor/rome/5-12-religion-culture-literature-art.asp?pg=20