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
Such relations no doubt existed at all times--around Comum, for instance, they were still the rule in the time of the empire--but as exceptional features in privileged districts and on humanely-managed estates. What we now refer to is the system of slavery on a great scale, which in the Roman state, as formerly in the Carthaginian, grew out of the ascendency of capital. While the captives taken in war and the hereditary transmission of slavery sufficed to keep up the stock of slaves during the earlier period, this system of slavery was, just like that of America, based on the methodically-prosecuted hunting of man; for, owing to the manner in which slaves were used with little regard to their life or propagation, the slave population was constantly on the wane, and even the wars which were always furnishing fresh masses to the slave-market were not sufficient to cover the deficit.
No country where this species of game could be hunted remained exempt from visitation; even in Italy it was a thing by no means unheard of, that the poor freeman was placed by his employer among the slaves. But the Negroland of that period was western Asia,(7) where the Cretan and Cilician corsairs, the real professional slave-hunters and slave- dealers, robbed the coasts of Syria and the Greek islands; and where, emulating their feats, the Roman revenue-farmers instituted human hunts in the client states and incorporated those whom they captured among their slaves.
7. It was asserted even then, that the human race in that quarter was pre-eminently fitted for slavery by its especial power of endurance. Plautus (Trin. 542) commends the Syrians: -genus quod patientissitmum est hominum-.
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Reference address : https://www.ellopos.net/elpenor/rome/4-02-reform-tiberius-gracchus.asp?pg=16