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
No course remained but to overawe the authors; on which account men well known and dangerous in a literary point of view, such as Publius Nigidius Figulus and Aulus Caecina, had more difficulty in obtaining permission to return to Italy than other exiles, while the oppositional writers tolerated in Italy were subjected to a practical censorship, the restraints of which were all the more annoying that the measure of punishment to be dreaded was utterly arbitrary.(4)
4. Any one who desires to compare the old and new hardships of authors will find opportunity of doing so in the letter of Caecina (Cicero, Aa. Fam. vi. 7).
The underground machinations of the overthrown parties against the new monarchy will be more fitly set forth in another connection. Here it is sufficient to say that risings of pretenders as well as of republicans were incessantly brewing throughout the Roman empire; that the flames of civil war kindled now by the Pompeians, now by the republicans, again burst forth brightly at various places; and that in the capital there was perpetual conspiracy against the life of the monarch. But Caesar could not be induced by these plots even to surround himself permanently with a body-guard, and usually contented himself with making known the detected conspiracies by public placards.
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Reference address : https://www.ellopos.net/elpenor/rome/5-11-old-republic-new-monarchy.asp?pg=22