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 Censorship a Prop of the Nobility
These circumstances explain, why the censorship became the pivot of the later republican constitution; why an office, originally standing by no means in the first rank, came to be gradually invested with external insignia which did not at all belong to it in itself and with an altogether unique aristocratic-republican glory, and was viewed as the crown and completion of a well-conducted public career; and why the government looked upon every attempt of the opposition to introduce their men into this office, or even to hold the censor responsible to the people for his administration during or after his term of office, as an attack on their palladium, and presented a united front of resistance to every such attempt.
It is sufficient in this respect to mention the storm which the candidature of Cato for the censorship provoked, and the measures, so extraordinarily reckless and in violation of all form, by which the senate prevented the judicial prosecution of the two unpopular censors of the year 550. But with their magnifying the glory of the censorship the government combined a characteristic distrust of this, their most important and for that very reason most dangerous, instrument.
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Reference address : https://www.ellopos.net/elpenor/rome/3-11-government-governed.asp?pg=11