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
Roman Early History of Rome
But as the first steps towards writing real history belonged to this period, to it belonged also the first attempts to record, and conventionally distort, the primitive history of Rome. The sources whence it was formed were of course the same as they are everywhere. Isolated names like those of the kings Numa, Ancus, Tullus, to whom the clan-names were probably only assigned subsequently, and isolated facts, such as the conquest of the Latins by king Tarquinius and the expulsion of the Tarquinian royal house, may have continued to live in true general tradition orally transmitted.
Further materials were furnished by the traditions of the patrician clans, such as the various tales that relate to the Fabii. Other tales gave a symbolic and historic shape to primitive national institutions, especially setting forth with great vividness the origin of rules of law. The sacredness of the walls was thus illustrated in the tale of the death of Remus, the abolition of blood-revenge in the tale of the end of king Tatius(15), the necessity of the arrangement as to the -pons sublicius- in the legend of Horatius Cocles,(15) the origin of the -provocatio- in the beautiful tale of the Horatii and Curiatii, the origin of manumission and of the burgess-rights of freedmen in the tale of the Tarquinian conspiracy and the slave Vindicius.
15. Cf. I. XI. Jurisdiction, second note.
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Reference address : https://www.ellopos.net/elpenor/rome/2-09-art-science.asp?pg=14