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
History of the Origin of Rome
In the legendary period the history of the origin of the city of Rome was set forth with great minuteness; and in its case the peculiar difficulty had to be surmounted, that there were, as we have already shown,(59) two wholly irreconcileable versions of it in circulation: the national version, which, in its leading outlines at least, was probably already embodied in the book of Annals, and the Greek version of Timaeus, which cannot have remained unknown to these Roman chroniclers.
59. Cf. II. IX. Roman Early History of Rome
The object of the former was to connect Rome with Alba, that of the latter to connect Rome with Troy; in the former accordingly the city was built by Romulus son of the Alban king, in the latter by the Trojan prince Aeneas. To the present epoch, probably either to Naevius or to Pictor, belongs the amalgamation of the two stories. The Alban prince Romulus remains the founder of Rome, but becomes at the same time the grandson of Aeneas; Aeneas does not found Rome, but is represented as bringing the Roman Penates to Italy and building Lavinium as their shrine, while his son Ascanius founds Alba Longa, the mother-city of Rome and the ancient metropolis of Latium.
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Reference address : https://www.ellopos.net/elpenor/rome/3-14-literature-art.asp?pg=90