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
Through whom, when, and how this comprehensive innovation came into existence, whether at once or gradually, whether through one or several authors, are questions to which we cannot furnish a satisfactory answer. We know only that this reform, as was natural, proceeded in the first instance from the urban court; that it first took formal shape in the instructions annually issued by the -praetor urbanus-, when entering on office, for the guidance of the parties in reference to the most important maxims of law to be observed in the judicial year then beginning (-edictum annuum- or -perpetuum praetoris urbani de iuris dictione-); and that, although various preparatory steps towards it may have been taken in earlier times, it certainly only attained its completion in this epoch.
The new code was theoretic and abstract, inasmuch as the Roman view of law had therein divested itself of such of its national peculiarities as it had become aware of; but it was at the same time practical and positive, inasmuch as it by no means faded away into the dim twilight of general equity or even into the pure nothingness of the so-called law of nature, but was applied by definite functionaries for definite concrete cases according to fixed rules, and was not merely capable of, but had already essentially received, a legal embodiment in the urban edict. This code moreover corresponded in matter to the wants of the time, in so far as it furnished the more convenient forms required by the increase of intercourse for legal procedure, for acquisition of property, and for conclusion of contracts.
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Reference address : https://www.ellopos.net/elpenor/rome/5-11-old-republic-new-monarchy.asp?pg=171