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
Class of Μέτοικοι Subsisting by the Side of the Community
At first, therefore, the burgesses were in reality the protectors, the non-burgesses were the protected; but in Rome as in all communities which freely admit settlement but do not throw open the rights of citizenship, it soon became a matter of increasing difficulty to harmonize this relation -de jure- with the actual state of things. The flourishing of commerce, the full equality of private rights guaranteed to all Latins by the Latin league (including even the acquisition of landed property), the greater frequency of manumissions as prosperity increased, necessarily occasioned even in peace a disproportionate increase of the number of μέτοικοι.
That number was further augmented by the greater part of the population of the neighbouring towns subdued by force of arms and incorporated with Rome; which, whether it removed to the city or remained in its old home now reduced to the rank of a village, ordinarily exchanged its native burgess-rights for those of a Roman μέτοικος. Moreover the burdens of war fell exclusively on the old burgesses and were constantly thinning the ranks of their patrician descendants, while the μέτοικοι shared in the results of victory without having to pay for it with their blood.
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Reference address : https://www.ellopos.net/elpenor/rome/1-06-burgesses-reformed-constitution.asp?pg=8