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
Once more--and for the last time--the poem of Lucretius is resonant
with the whole poetic pride and the whole poetic earnestness
of the sixth century, in which, amidst the images of the formidable
Carthaginian and the glorious Scipiad, the imagination of the poet
is more at home than in his own degenerate age.(18)
18. This naively appears in the descriptions of war, in which
the seastorms that destroy armies, and the hosts of elephants that
trample down those who are on their own side--pictures, that is,
from the Punic wars--appear as if they belong to the immediate
present. Comp. ii. 41; v. 1226, 1303, 1339.
To him too
his own song "gracefully welling up out of rich feeling" sounds,
as compared with the common poems, "like the brief song of the swan
compared with the cry of the crane";--with him too the heart swells,
listening to the melodies of its own invention, with the hope
of illustrious honours--just as Ennius forbids the men to whom
he "gave from the depth of the heart a foretaste of fiery song,"
to mourn at his, the immortal singer's, tomb.