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
It was not until the present period that
the Atellan piece was handed over to actors properly so called,(12)
and was employed, like the Greek satyric drama, as an afterpiece
particularly after tragedies; a change which naturally suggested
the extension of literary activity to that field.
12. In the time of the empire the Atellana was represented by
professional actors (Friedlander in Becker's Handbuch. vi. 549).
The time at which these began to engage in it is not reported, but
it can hardly have been other than the time at which the Atellan
was admitted among the regular stage-plays, i. e. the epoch before
Cicero (Cic. ad Fam. ix. 16). This view is not inconsistent with
the circumstance that still in Livy's time (vii. 2) the Atellan
players retained their honorary rights as contrasted with other
actors; for the statement that professional actors began to take
part in performing the Atellana for pay does not imply that
the Atellana was no longer performed, in the country towns
for instance, by unpaid amateurs, and the privilege therefore
still remained applicable,