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
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
The Carthaginian Dominion in Africa
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.
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Reference address : https://www.ellopos.net/elpenor/rome/3-01-carthage.asp?pg=12