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
In Rome on the other hand no serious preparations had been made. It was reported, indeed, that restless movements were occurring in Italy, and that the communities of the allies maintained a remarkable intercourse with each other; but instead of calling the citizens in all haste to arms, the governing corporation contented itself with exhorting the magistrates in the customary fashion to watchfulness and with sending out spies to learn farther particulars.
The capital was so totally undefended, that a resolute Marsian officer Quintus Pompaedius Silo, one of the most intimate friends of Drusus, is said to have formed the design of stealing into the city at the head of a band of trusty associates carrying swords under their clothes, and of seizing it by a coup de main. Preparations were accordingly made for a revolt; treaties were concluded, and arming went on silently but actively, till at last, as usual, the insurrection broke out through an accident somewhat earlier than the leading men had intended.
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Reference address : https://www.ellopos.net/elpenor/rome/4-07-sulpician-revolution.asp?pg=15