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
If we inquire into the basis of the duodecimal system and consider
how it can have happened that, in addition to ten, twelve should
have been so early and universally singled out from the equal series
of numbers, we shall probably be able to find no other source to
which it can be referred than a comparison of the solar and lunar
periods.
Still more than the double hand of ten fingers did the
solar cycle of nearly twelve lunar periods first suggest to man
the profound conception of an unit composed of equal units, and
thereby originate the idea of a system of numbers, the first step
towards mathematical thought.
The consistent duodecimal development
of this idea appears to have belonged to the Italian nation, and
to have preceded the first contact with the Greeks.
