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
Thus Sicily even
from the Carthaginian period formed a closed customs-district, on
the frontier of which a tax of 5 per cent on the value was levied
from all imports or exports; thus on the frontiers of Asia there
was levied in consequence of the Sempronian law(10) a similar tax
of 21 per cent; in like manner the province of Narbo, exclusively
the domain of the Roman colony, was organized as a Roman customs-
district This arrangement, besides its fiscal objects, may have
been partly due to the commendable purpose of checking the
confusion inevitably arising out of a variety of communal tolls by
a uniform regulation of frontier-dues. The levying of the customs,
like that of the tenths, was without exception leased to middlemen.
