Slaves to the definition are we? Chained to the dictionary as to the great and heavy oar?
The value of slaves historically has been tied to their availability and utility. Rome in full get-you-conquer-on mode had surplus; they were disposable, readily cycled into the salt mines with the bones spit out in months or years at the most. As the expansion slowed, so did the flow of new slaves, and the value rose; a small subset of slaves were rolled in the administrations of Tiberius and Claudius (his freedman Narcissus cleaned up the Messalina he made.) - the slave bureaucracy, but this only represented a small portion of the entire slave population - freedmen - slaves who earned enough to purchase their freedom were not particularly common.
Indentured servants were the best of both worlds for the truly unscrupulous - rather than slaves, whose maintenance was tied to specific standards, indentured servants could be worked to death; which was cheaper and more economically viable than the payout at the end of their term.
The value of slaves historically has been tied to their availability and utility. Rome in full get-you-conquer-on mode had surplus; they were disposable, readily cycled into the salt mines with the bones spit out in months or years at the most. As the expansion slowed, so did the flow of new slaves, and the value rose; a small subset of slaves were rolled in the administrations of Tiberius and Claudius (his freedman Narcissus cleaned up the Messalina he made.) - the slave bureaucracy, but this only represented a small portion of the entire slave population - freedmen - slaves who earned enough to purchase their freedom were not particularly common.
Indentured servants were the best of both worlds for the truly unscrupulous - rather than slaves, whose maintenance was tied to specific standards, indentured servants could be worked to death; which was cheaper and more economically viable than the payout at the end of their term.