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
That this new government of the senate amidst all its retention of existing forms involved a complete revolutionizing of the old commonwealth, is clear. That the free action of the burgesses should be arrested and benumbed; that the magistrates should be reduced to be the presidents of its sittings and its executive commissioners; that a corporation for the mere tendering of advice should seize the inheritance of both the authorities sanctioned by the constitution and should become, although under very modest forms, the central government of the state--these were steps of revolution and usurpation.
Nevertheless, if any revolution or any usurpation appears justified before the bar of history by exclusive ability to govern, even its rigorous judgment must acknowledge that this corporation timeously comprehended and worthily fulfilled its great task.
Called to power not by the empty accident of birth, but substantially by the free choice of the nation; confirmed every fifth year by the stern moral judgment of the worthiest men; holding office for life, and so not dependent on the expiration of its commission or on the varying opinion of the people; having its ranks close and united ever after the equalization of the orders; embracing in it all the political intelligence and practical statesmanship that the people possessed; absolute in dealing with all financial questions and in the guidance of foreign policy; having complete power over the executive by virtue of its brief duration and of the tribunician intercession which was at the service of the senate after the termination of the quarrels between the orders--the Roman senate was the noblest organ of the nation, and in consistency and political sagacity, in unanimity and patriotism, in grasp of power and unwavering courage, the foremost political corporation of all times--still even now an "assembly of kings," which knew well how to combine despotic energy with republican self-devotion.
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Reference address : https://www.ellopos.net/elpenor/rome/2-03-equalization-orders-aristocracy.asp?pg=62