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
The most ancient priesthoods in the community bore reference to Mars; especially the priest of the god of the community, nominated for life, "the kindler of Mars" (-flamen Martialis-) as he was designated from presenting burnt-offerings, and the twelve "leapers" (-salii-), a band of young men who in March performed the war-dance in honour of Mars and accompanied it by song. We have already explained(5) how the amalgamation of the Hill-community with that of the Palatine gave rise to the duplication of the Roman Mars, and thereby to the introduction of a second priest of Mars--the -flamen Quirinalis- --and a second guild of dancers--the -salii collini-.
5. Cf. I. IV. Tities and Luceres
To these were added other public worships (some of which probably had an origin far earlier than that of Rome), for which either single priests were appointed--as those of Carmentis, of Volcanus, of the god of the harbour and the river--or the celebration of which was committed to particular colleges or clans in name of the people.
Such a college was probably that of the twelve "field-brethren" (-fratres arvales-) who invoked the "creative goddess" (-dea dia-) in May to bless the growth of the seed; although it is very doubtful whether they already at this period enjoyed that peculiar consideration which we find subsequently accorded to them in the time of the empire.
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Reference address : https://www.ellopos.net/elpenor/rome/1-12-religion.asp?pg=12