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
But notwithstanding these enlargements of the powers of the
burgess-assemblies, their practical influence on state affairs began,
particularly towards the close of this period, to wane. First of all,
the extension of the bounds of Rome deprived her primary assembly of
its true basis. As an assembly of the freeholders of the community,
it formerly might very well meet in sufficiently full numbers, and
might very well know its own wishes, even without discussion; but the
Roman burgess-body had now become less a civic community than a state.
The fact that those dwelling together voted also with each other, no
doubt, introduced into the Roman comitia, at least when the voting
was by tribes, a sort of inward connection and into the voting now
and then energy and independence; but under ordinary circumstances
the composition of the comitia and their decision were left dependent
on the person who presided or on accident, or were committed to the
hands of the burgesses domiciled in the capital.