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
It was no wonder, accordingly, that the mercantile spirit took possession of the nation, or rather--for that was no new thing in Rome--that the spirit of the capitalist now penetrated and pervaded all other aspects and stations of life, and agriculture as well as the government of the state began to become enterprises of capitalists. The preservation and increase of wealth quite formed a part of public and private morality. "A widow's estate may diminish;" Cato wrote in the practical instructions which he composed for his son, "a man must increase his means, and he is deserving of praise and full of a divine spirit, whose account-books at his death show that he has gained more than he has inherited."
Wherever, therefore, there was giving and counter-giving, every transaction although concluded without any sort of formality was held as valid, and in case of necessity the right of action was accorded to the party aggrieved if not by the law, at any rate by mercantile custom and judicial usage;(24) but the promise of a gift without due form was null alike in legal theory and in practice.
24. On this was based the actionable character of contracts of buying, hiring, and partnership, and, in general, the whole system of non-formal actionable contracts.
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Reference address : https://www.ellopos.net/elpenor/rome/3-12-management-land-capital.asp?pg=34