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
This was
done first by the younger Cato (d. about 600) and by Marcus Brutus
(nearly contemporary); and these collections were, as it would
appear, arranged in the order of matters.(39)
39. Cato's book probably bore the title -De iuris disciplina-
(Gell. xiii. 20), that of Brutus the title -De iure civili- (Cic.
pro Cluent. 51, 141; De Orat. ii. 55, 223); that they were
essentially collections of opinions, is shown by Cicero (De Orat.
ii. 33, 142).
A strictly
systematic treatment of the law of the land soon followed.
Its founder was the -pontifex maximus- Quintus Mucius Scaevola
(consul in 659, d. 672),(40) in whose family jurisprudence was,
like the supreme priesthood, hereditary.