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
It is important, on account of the subsequent course of development, to note these first steps towards the centuries taking part in public affairs; but the centuries came to acquire such rights at first more in the way of natural sequence than of direct design, and subsequently to the Servian reform, as before, the assembly of the curies was regarded as the proper burgess-community, whose homage bound the whole people in allegiance to the king. By the side of these new landowning full-burgesses stood the domiciled foreigners from the allied Latium, as participating in the public burdens, tribute and task-works (hence -municipes-); while the burgesses not domiciled, who were beyond the pale of the tribes, and had not the right to serve in war and vote, came into view only as "owing tribute" (-aerarii-).
In this way, while hitherto there had been distinguished only two classes of members of the community, burgesses and clients, there were now established those three political classes, which exercised a dominant influence over the constitutional law of Rome for many centuries.
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Reference address : https://www.ellopos.net/elpenor/rome/1-06-burgesses-reformed-constitution.asp?pg=20