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
This is
not yet the place for a description of this regenerated empire of
Cyrus; it is sufficient to mention generally the fact that powerful
as was the influence of Hellenism in its composition, the Parthian
state, as compared with that of the Seleucids, was based on a national
and religious reaction, and that the old Iranian language, the order
of the Magi and the worship of Mithra, the Oriental feudatory system,
the cavalry of the desert and the bow and arrow, first emerged there
in renewed and superior opposition to Hellenism. The position of the
imperial kings in presence of all this was really pitiable.
The family
of the Seleucids was by no means so enervated as that of the Lagids
for instance, and individuals among them were not deficient in
valour and ability; they reduced, it may be, one or another of those
numerous rebels, pretenders, and intermeddlers to due bounds; but
their dominion was so lacking in a firm foundation, that they were
unable to impose even a temporary check on anarchy. The result was
inevitable.