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 patrician body still subsisted, although without essential privileges as an order, in the character of a close aristocratic guild;(19) but as it could receive no new -gentes-(20) it had dwindled away more and more in the course of centuries, and in the time of Caesar there were not more than fifteen or sixteen patrician -gentes- still in existence.
19. Cf. II. III. Union of the Plebeians
20. Cf. II. I. The New Community
Caesar, himself sprung from one of them, got the right of creating new patrician -gentes- conferred on the Imperator by decree of the people, and so established, in contrast to the republican nobility, the new aristocracy of the patriciate, which most happily combined all the requisites of a monarchical aristocracy--the charm of antiquity, entire dependence on the government, and total insignificance. On all sides the new sovereignty revealed itself.
Under a monarch thus practically unlimited there could hardly be scope for a constitution at all--still less for a continuance of the hitherto existing commonwealth based on the legal co-operation of the burgesses, the senate, and the several magistrates. Caesar fully and definitely reverted to the tradition of the regal period; the burgess-assembly remained--what it had already been, in that period-- by the side of and with the king the supreme and ultimate expression of the will of the sovereign people; the senate was brought back to its original destination of giving advice to the ruler when he requested it; and lastly the ruler concentrated in his person anew the whole magisterial authority, so that there existed no other independent state-official by his side any more than by the side of the kings of the earliest times.
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Reference address : https://www.ellopos.net/elpenor/rome/5-11-old-republic-new-monarchy.asp?pg=43