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
He supported it, partly in literature--as when he combated the first coalition, the "three-headed monster," in pamphlets; partly in more serious warfare, where we found him in the army of Pompeius as commandant of Further Spain.(22)
22. Cf. V. X. The Pompeians in Spain
When the cause of the republic was lost, Varro was destined by his conqueror to be librarian of the library which was to be formed in the capital. The troubles of the following period drew the old man once more into their vortex, and it was not till seventeen years after Caesar's death, in the eighty-ninth year of his well-occupied life, that death called him away.
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Reference address : https://www.ellopos.net/elpenor/rome/5-12-religion-culture-literature-art.asp?pg=57