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
Abolition of the Life-Presidency of the Community
As the Servian reform, which placed the μέτοικος on a footing of equality in a military point of view with the burgess, appears to have originated from considerations of an administrative nature rather than from any political party-tendency, we may assume that the first of the movements which led to internal crises and changes of the constitution was that which sought to limit the magistracy. The earliest achievement of this, the most ancient opposition in Rome, consisted in the abolition of the life-tenure of the presidency of the community; in other words, in the abolition of the monarchy.
How necessarily this was the result of the natural development of things, is most strikingly demonstrated by the fact, that the same change of constitution took place in an analogous manner through the whole circuit of the Italo-Greek world. Not only in Rome, but likewise among the other Latins as well as among the Sabellians, Etruscans, and Apulians--and generally, in all the Italian communities, just as in those of Greece--we find the rulers for life of an earlier epoch superseded in after times by annual magistrates.
In the case of the Lucanian canton there is evidence that it had a democratic government in time of peace, and it was only in the event of war that the magistrates appointed a king, that is, an official similar to the Roman dictator. The Sabellian civic communities, such as those of Capua and Pompeii, in like manner were in later times governed by a "community-manager" (-medix tuticus-) changed from year to year, and we may assume that similar institutions existed among the other national and civic communities of Italy.
In this light the reasons which led to the substitution of consuls for kings in Rome need no explanation. The organism of the ancient Greek and Italian polity developed of itself by a sort of natural necessity the limitation of the life-presidency to a shortened, and for the most part an annual, term. Simple, however, as was the cause of this change, it might be brought about in various ways; a resolution might be adopted on the death of one life-ruler not to elect another--a course which the Roman senate is said to have attempted after the death of Romulus; or the ruler might voluntarily abdicate, as is alleged to have been the intention of king Servius Tullius; or the people might rise in rebellion against a tyrannical ruler, and expel him.
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Reference address : https://www.ellopos.net/elpenor/rome/2-01-constitution-magistrate.asp?pg=3