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
Whether what we call metre existed in the earlier times is doubtful; the litany of the Arval Brethren scarcely accommodates itself to an outwardly fixed metrical system, and presents to us rather the appearance of an animated recitation. On the other hand we find in subsequent times a very ancient rhythm, the so-called Saturnian(6) or Faunian metre, which is foreign to the Greeks, and may be conjectured to have arisen contemporaneously with the oldest Latin popular poetry.
6. The name probably denotes nothing but "the chant-measure," inasmuch as the -satura- was originally the chant sung at the carnival (II. Art). The god of sowing, -Saeturnus- or -Saiturnus-, afterwards -Saturnus-, received his name from the same root; his feast, the Saturnalia, was certainly a sort of carnival, and it is possible that the farces were originally exhibited chiefly at this feast.
But there are no proofs of a relation between the Satura and the Saturnalia, and it may be presumed that the immediate association of the -versus saturnius- with the god Saturn, and the lengthening of the first syllable in connection with that view, belong only to later times.
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Reference address : https://www.ellopos.net/elpenor/rome/1-15-art.asp?pg=10