The slaves consisted, for the most part, of barbarian captives, [451] taken in thousands by the chance of war, purchased at a vile price, [46] accustomed to a life of independence, and impatient to break and to revenge their fetters.
Against such internal enemies, whose desperate insurrections had more than once reduced the republic to the brink of destruction, [47] the most severe [471] regulations, [48] and the most cruel treatment, seemed almost justified by the great law of self-preservation.

But when the principal nations of Europe, Asia, and Africa were united under the laws of one sovereign, the source of foreign supplies flowed with much less abundance, and the Romans were reduced to the milder but more tedious method of propagation.

[481] In their numerous families, and particularly in their country estates, they encouraged the marriage of their slaves.
[482] The sentiments of nature, the habits of education, and the possession of a dependent species of property, contributed to alleviate the hardships of servitude.

[49] The existence of a slave became an object of greater value, and though his happiness still depended on the temper and circumstances of the master, the humanity of the latter, instead of being restrained by fear, was encouraged by the sense of his own interest.

The progress of manners was accelerated by the virtue or policy of the emperors; and by the edicts of Hadrian and the Antonines, the protection of the laws was extended to the most abject part of mankind.