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
That they did so cannot of course be strictly
proved; but as the use of masks for the face in Latium in the case
of the national drama was of immemorial antiquity, while the Greek
drama in Rome did not adopt them for a century after its first
establishment, as, moreover, those Atellane masks were of decidedly
Italian origin, and as, in fine, the origination as well as
the execution of improvised pieces cannot well be conceived apart
from fixed masks assigning once for all to the player his proper
position throughout the piece, we must associate fixed masks with
the rudiments of the Roman drama, or rather regard them as constituting
those rudiments themselves.
Earliest Greek Influences
If our information respecting the earliest indigenous culture and
art of Latium is so scanty, it may easily be conceived that our
knowledge will be still scantier regarding the earliest impulses
imparted in this respect to the Romans from without. In a certain
sense we may include under this head their becoming acquainted with
foreign languages, particularly the Greek.