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 Italy it was Marcus Tullius Cicero (648-711) who, after having in his early youth gone along with the Hortensian manner, was brought by hearing the Rhodian masters and by his own more matured taste to better paths, and thenceforth addicted himself to strict purity of language and the thorough periodic arrangement and modulation of his discourse. The models of language, which, in this respect he followed, he found especially in those circles of the higher Roman society which had suffered but little or not at all from vulgarism; and, as was already said, there were still such, although they were beginning to disappear.
The earlier Latin and the good Greek literature, however considerable was the influence of the latter more especially on the rhythm of his oratory, were in this matter only of secondary moment: this purifying of the language was by no means a reaction of the language of books against that of conversation, but a reaction of the language of the really cultivated against the jargon of spurious and partial culture.
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Reference address : https://www.ellopos.net/elpenor/rome/5-12-religion-culture-literature-art.asp?pg=17