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
Conservative Character of the Revolution
We thus see that in the Roman commonwealth, even on the conversion of the monarchy into a republic, the old was as far as possible retained. So far as a revolution in a state can be conservative at all, this one was so; not one of the constituent elements of the commonwealth was really overthrown by it. This circumstance indicates the character of the whole movement.
The expulsion of the Tarquins was not, as the pitiful and deeply falsified accounts of it represent, the work of a people carried away by sympathy and enthusiasm for liberty, but the work of two great political parties already engaged in conflict, and clearly aware that their conflict would steadily continue--the old burgesses and the μέτοικοι --who, like the English Whigs and Tories in 1688, were for a moment united by the common danger which threatened to convert the commonwealth into the arbitrary government of a despot, and differed again as soon as the danger was over.
The old burgesses could not get rid of the monarchy without the cooperation of the new burgesses; but the new burgesses were far from being sufficiently strong to wrest the power out of the hands of the former at one blow. Compromises of this sort are necessarily limited to the smallest measure of mutual concessions obtained by tedious bargaining; and they leave the future to decide which of the constituent elements shall eventually preponderate, and whether they will work harmoniously together or counteract one another.
To look therefore merely to the direct innovations, possibly to the mere change in the duration of the supreme magistracy, is altogether to mistake the broad import of the first Roman revolution: its indirect effects were by far the most important, and vaster doubtless than even its authors anticipated.
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Reference address : https://www.ellopos.net/elpenor/rome/2-01-constitution-magistrate.asp?pg=27