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
The sixth century was, both in a political and a literary point of
view, a vigorous and great age. It is true that we do not find in
the field of authorship any more than in that of politics a man of
the first rank; Naevius, Ennius, Plautus, Cato, gifted and lively
authors of distinctly-marked individuality, were not in the highest
sense men of creative talent; nevertheless we perceive in the
soaring, stirring, bold strain of their dramatic, epic, and
historic attempts, that these rest on the gigantic struggles of
the Punic wars.
Much is only artificially transplanted, there
are various faults in delineation and colouring, the form of art
and the language are deficient in purity of treatment, Greek and
national elements are quaintly conjoined; the whole performance
betrays the stamp of its scholastic origin and lacks independence
and completeness; yet there exists in the poets and authors of that
age, if not the full power to reach their high aim, at any rate
the courage to compete with and the hope of rivalling the Greeks.
It is otherwise in the epoch before us.