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
No remains have been preserved of these -incunabula- of the Roman epos and drama. That the ancestral lays were traditional is self-evident, and is abundantly demonstrated by the fact that they were regularly recited by children; but even in the time of Cato the Elder they had completely passed into oblivion.
The comedies again, if it be allowable so to name them, were at this period and long afterwards altogether improvised. Consequently nothing of this popular poetry and popular melody could be handed down but the measure, the accompaniment of music and choral dancing, and perhaps the masks.
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Reference address : https://www.ellopos.net/elpenor/rome/1-15-art.asp?pg=9