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
In Rome, Polybius tells us, nobody gives to any one unless he must do so, and no one pays a penny before it falls due, even among near relatives. The very legislation yielded to this mercantile morality, which regarded all giving away without recompense as squandering; the giving of presents and bequests and the undertaking of sureties were subjected to restriction at this period by decree of the burgesses, and heritages, if they did not fall to the nearest relatives, were at least taxed. In the closest connection with such views mercantile punctuality, honour, and respectability pervaded the whole of Roman life. Every ordinary man was morally bound to keep an account-book of his income and expenditure--in every well-arranged house, accordingly, there was a separate account-chamber (-tablinum-)--and every one took care that he should not leave the world without having made his will: it was one of the three matters in his life which Cato declares that he regretted, that he had been a single day without a testament.
Those household books were universally by Roman usage admitted as valid evidence in a court of justice, nearly in the same way as we admit the evidence of a merchant's ledger. The word of a man of unstained repute was admissible not merely against himself, but also in his own favour; nothing was more common than to settle differences between persons of integrity by means of an oath demanded by the one party and taken by the other--a mode of settlement which was reckoned valid even in law; and a traditional rule enjoined the jury, in the absence of evidence, to give their verdict in the first instance for the man of unstained character when opposed to one who was less reputable, and only in the event of both parties being of equal repute to give it in favour of the defendant.(25)
25. The chief passage as to this point is the fragment of Cato in Gellius, xiv. 2. In the case of the -obligatio litteris- also, i. e. a claim based solely on the entry of a debt in the account-book of the creditor, this legal regard paid to the personal credibility of the party, even where his testimony in his own cause is concerned, affords the key of explanation; and hence it happened that in later times, when this mercantile repute had vanished from Roman life, the -obligatio litteris-, while not exactly abolished, fell of itself into desuetude.
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Reference address : https://www.ellopos.net/elpenor/rome/3-12-management-land-capital.asp?pg=35