The Law of Slavery
In the law of persons the first division is into freemen (liberi) and slaves (servi).
Freedom, says Justinian, "is a man's natural power of doing what he pleases, so far as he is not prevented by force or law. Slavery is an institution of the law of nations, against nature, subjecting one man to the dominion of another."
The Romans thus recognized slavery as an artificial institution, contrary to the law of nature, but it persisted in Rome down to the latest times.