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
It was probably the reflex influence of these successes abroad,
that first led the Carthaginians to change the character of their
occupation in Africa from a tenure of hire and sufferance to one of
proprietorship and conquest. It appears to have been only about the
year 300 of Rome that the Carthaginian merchants got rid of the rent
for the soil, which they had hitherto been obliged to pay to the
natives. This change enabled them to prosecute a husbandry of their
own on a great scale.
From the outset the Phoenicians had been
desirous to employ their capital as landlords as well as traders,
and to practise agriculture on a large scale by means of slaves or
hired labourers; a large portion of the Jews in this way served the
merchant-princes of Tyre for daily wages. Now the Carthaginians
could without restriction extract the produce of the rich Libyan soil
by a system akin to that of the modern planters; slaves in chains
cultivated the land--we find single citizens possessing as many as
twenty thousand of them.