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
We are less able to trace the progress of the religious conceptions of
the Romans during this epoch. In general they adhered with simplicity
to the simple piety of their ancestors, and kept equally aloof from
superstition and from unbelief. How vividly the idea of spiritualizing
all earthly objects, on which the Roman religion was based, still
prevailed at the close of this epoch, is shown by the new "God of
silver" (-Argentinus-), who presumably came into existence only in
consequence of the introduction of the silver currency in 485, and who
naturally was the son of the older "God of copper" (-Aesculanus-).
The relations to foreign lands were the same as heretofore; but here,
and here especially, Greek influences were on the increase. It was
only now that temples began to rise in Rome itself in honour of the
Greek gods. The oldest was the temple of Castor and Pollux, which
had been vowed in the battle at lake Regillus(17) and was consecrated
on 15th July 269.