Slavery in Graeco-Roman Times

In the Hellenistic world, opinions about slavery were different from later views in the Roman world. Aristotle, for example, speaks of slaves as “speaking implements” (Aristotle, Politica 1.1-7): slaves are slaves by nature.
In Roman times, slaves and free men are declared to be equal in principle: to be a slave is not a natural matter but a question of the lot that is dealt to you. But still in the Roman world as well, slavery was held to be completely legitimate and morally justified.