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
Speeches and Letters
Contemporaneously with historical literature, and in some sense as an appendage to it, arose the literature of speeches and letters. This in like manner was commenced by Cato; for the Romans possessed nothing of an earlier age except some funeral orations, most of which probably were only brought to light at a later period from family archives, such as that which the veteran Quintus Fabius, the opponent of Hannibal, delivered when an old man over his son who had died in his prime.
Cato on the other hand committed to writing in his old age such of the numerous orations which he had delivered during his long and active public career as were historically important, as a sort of political memoirs, and published them partly in his historical work, partly, it would seem, as independent supplements to it. There also existed a collection of his letters.
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Reference address : https://www.ellopos.net/elpenor/rome/3-14-literature-art.asp?pg=95