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
On the other hand it must have been at this period, when the
indication and redaction of law began, that the Roman technical style
first established itself--a style which at least in its developed
shape is nowise inferior to the modern legal phraseology of England in
stereotyped formulae and turns of expression, endless enumeration of
particulars, and long-winded periods; and which commends itself to the
initiated by its clearness and precision, while the layman who does
not understand it listens, according to his character and humour, with
reverence, impatience, or chagrin.
Philology
Moreover at this epoch began the treatment of the native languages
after a rational method. About its commencement the Sabellian as well
as the Latin idiom threatened, as we saw,(25) to become barbarous,
and the abrasion of endings and the corruption of the vowels and more
delicate consonants spread on all hands, just as was the case with the
Romanic languages in the fifth and sixth centuries of the Christian
era.