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
Philosophy, in fine, was not yet represented in literature, since neither did an inward need develop a national Roman philosophy nor did outward circumstances call forth a Latin philosophical authorship. It cannot even be shown with certainty that there were Latin translations of popular summaries of philosophy belonging to this period; those who pursued philosophy read and disputed in Greek.
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Reference address : https://www.ellopos.net/elpenor/rome/4-13-literature-art.asp?pg=56