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
Equality of the Burgesses
Sternly defined as was the contrast between burgess and non-burgess, the equality of rights within the burgess-body was complete. No people has ever perhaps equalled that of Rome in the inexorable rigour with which it has carried out these principles, the one as fully as the other. The strictness of the Roman distinction between burgesses and non-burgesses is nowhere perhaps brought out with such clearness as in the treatment of the primitive institution of honorary citizenship, which was originally designed to mediate between the two.
When a stranger was, by resolution of the community, adopted into the circle of the burgesses, he might surrender his previous citizenship, in which case he passed over wholly into the new community; but he might also combine his former citizenship with that which had just been granted to him. Such was the primitive custom, and such it always remained in Greece, where in later ages the same person not unfrequently held the freedom of several communities at the same time.
But the greater vividness with which the conception of the community as such was realized in Latium could not tolerate the idea that a man might simultaneously belong in the character of a burgess to two communities; and accordingly, when the newly-chosen burgess did not intend to surrender his previous franchise, it attached to the nominal honorary citizenship no further meaning than that of an obligation to befriend and protect the guest (-jus hospitii-), such as had always been recognized as incumbent in reference to foreigners.
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Reference address : https://www.ellopos.net/elpenor/rome/1-05-original-constitution-rome.asp?pg=17