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
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
These were well known also in Rome; in amateur performances the players appeared without exception masked. But the actors who were to perform the Greek comedies in Rome were not supplied with the masks--beyond doubt much more artificial--that were necessary for them; a circumstance which, apart from all else in connection with the defective acoustic arrangements of the stage,(26) not only compelled the actor to exert his voice unduly, but drove Livius to the highly inartistic but inevitable expedient of having the portions which were to be sung performed by a singer not belonging to the staff of actors, and accompanied by the mere dumb show of the actor within whose part they fell.
26. Even when the Romans built stone theatres, these had not the sounding-apparatus by which the Greek architects supported the efforts of the actors (Vitruv. v. 5, 8).
As little were the givers of the Roman festivals disposed to put themselves to material expense for decorations and machinery. The Attic stage regularly presented a street with houses in the background, and had no shifting decorations; but, besides various other apparatus, it possessed more especially a contrivance for pushing forward on the chief stage a smaller one representing the interior of a house. The Roman theatre, however, was not provided with this; and we can hardly therefore throw the blame on the poet, if everything, even childbirth, was represented on the street.
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Reference address : https://www.ellopos.net/elpenor/rome/3-14-literature-art.asp?pg=44