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
Of a kindred character was the proposal, which Cato made in the
senate, to remedy the decline of the burgess-cavalry by the
institution of four hundred new equestrian stalls.(57)
The exchequer
cannot have wanted means for the purpose; but the proposal appears to
have been thwarted by the exclusive spirit of the nobility and their
endeavour to remove from the burgess-cavalry those who were troopers
merely and not knights. On the other hand, the serious emergencies of
the war, which even induced the Roman government to make an attempt
--fortunately unsuccessful--to recruit their armies after the Oriental
fashion from the slave-market,(58) compelled them to modify the
qualifications hitherto required for service in the burgess-army, viz.
a minimum census of 11,000 -asses- (43 pounds), and free birth.