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
The late praetor Lucius Catilina, and the quaestor Gnaeus Piso, were distinguished among their fellows not merely by their genteel birth and their superior rank. They had broken down the bridge completely behind them, and impressed their accomplices by their dissoluteness quite as much as by their talents. Catilina especially was one of the most wicked men in that wicked age. His villanies belong to the records of crime, not to history; but his very outward appearance--the pale countenance, the wild glance, the gait by turns sluggish and hurried--betrayed his dismal past. He possessed in a high degree the qualities which are required in the leader of such a band-- the faculty of enjoying all pleasures and of bearing all privations, courage, military talent, knowledge of men, the energy of a felon, and that horrible mastery of vice, which knows how to bring the weak to fall and how to train the fallen to crime.
To form out of such elements a conspiracy for the overthrow of the existing order of things could not be difficult to men who possessed money and political influence. Catilina, Piso, and their fellows entered readily into any plan which gave the prospect of proscriptions and cancelling of debtor-books; the former had moreover special hostility to the aristocracy, because it had opposed the candidature of that infamous and dangerous man for the consulship. As he had formerly in the character of an executioner of Sulla hunted the proscribed at the head of a band of Celts and had killed among others his own aged father-in-law with his own hand, he now readily consented to promise similar services to the opposite party. A secret league was formed. The number of individuals received into it is said to have exceeded 400; it included associates in all the districts and urban communities of Italy; besides which, as a matter of course, numerous recruits would flock unbidden from the ranks of the dissolute youth to an insurrection, which inscribed on its banner the seasonable programme of wiping out debts.
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Reference address : https://www.ellopos.net/elpenor/rome/5-05-parties-pompeius.asp?pg=16