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
Saturninus and Glaucia sought to control the more important consular election by the expedient for the removal of inconvenient competitors which had been tried in the previous year; the counter-candidate of the government party, Gaius Memmius--the same who eleven years before had led the opposition against them(9)--was suddenly assailed by a band of ruffians and beaten to death.
9. Cf. IV. IV. Treaty between Rome and Numidia
But the government party had only waited for a striking event of this sort in order to employ force. The senate required the consul Gaius Marius to interfere, and the latter in reality professed his readiness now to draw for the conservative party the sword, which he had obtained from the democracy and had promised to wield on its behalf. The young men were hastily called out, equipped with arms from the public buildings, and drawn up in military array; the senate itself appeared under arms in the Forum, with its venerable chief Marcus Scaurus at its head.
The opposite party were doubtless superior in a street-riot, but were not prepared for such an attack; they had now to defend themselves as they could. They broke open the doors of the prisons, and called the slaves to liberty and to arms; they proclaimed-- so it was said at any rate--Saturninus as king or general; on the day when the new tribunes of the people had to enter on their office, the 10th of December 654, a battle occurred in the great market-place--the first which, since Rome existed, had ever been fought within the walls of the capital. The issue was not for a moment doubtful.
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Reference address : https://www.ellopos.net/elpenor/rome/4-06-marius-revolution-drusus-reform.asp?pg=31