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
Much however as the city of Rome gained by the new order of things in commodiousness and magnificence, its political supremacy was, as we have already said, lost to it irrecoverably through that very change. The idea that the Roman state should coincide with the city of Rome had indeed in the course of time become more and more unnatural and preposterous; but the maxim had been so intimately blended with the essence of the Roman republic, that it could not perish before the republic itself.
It was only in the new state of Caesar that it was, with the exception perhaps of some legal fictions, completely set aside, and the community of the capital was placed legally on a level with all other municipalities; indeed Caesar--here as everywhere endeavouring not merely to regulate the thing, but also to call it officially by the right name-- issued his Italian municipal ordinance, beyond doubt purposely, at once for the capital and for the other urban communities. We may add that Rome, just because it was incapable of a living communal character as a capital, was even essentially inferior to the other municipalities of the imperial period.
The republican Rome was a den of robbers, but it was at the same time the state; the Rome of the monarchy, although it began to embellish itself with all the glories of the three continents and to glitter in gold and marble, was yet nothing in the state but a royal residence in connection with a poor-house, or in other words a necessary evil.
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Reference address : https://www.ellopos.net/elpenor/rome/5-11-old-republic-new-monarchy.asp?pg=96