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 final step was
taken eight years afterwards (643), when by a new decree of the
people(3) the occupied domain-land was directly converted into the
rent-free private property of the former occupants.
3. It is in great part still extant and known under the erroneous
name, which has now been handed down for three hundred years,
of the Thorian agrarian law.
It was added,
that in future domain-land was not to be occupied at all, but was
either to be leased or to lie open as public pasture; in the latter
case provision was made by the fixing of a very low maximum of ten
head of large and fifty head of small cattle, that the large herd-
owner should not practically exclude the small. In these judicious
regulations the injurious character of the occupation-system, which
moreover was long ago given up,(4) was at length officially recognized,
but unhappily they were only adopted when it had already deprived the
state in substance of its domanial possessions.