Slavery is one of the most peculiar characteristic of the ancient Roman society and economy. With ragards to this aspects, there are however many misunderstandings and prejudices: slavery in Ancient Rome had nothing in common with the modern concept of slavery i.e. the forms of slavery diffused in North America.
Ancient slavery had no racial or national feature (these concepts were totally unknown to the civis romanvs) also because the idea of "slave" had deeper and more existential reasons.
It is important to note that in Ancient Rome, nobody was a "human being" by birth: it was necessary to become a member of the human consortium. Children actually remained out of the human dimension: they were in a lower condition. It was not a question of being an adult: to be a real man or woman it was necessary a "passage phase" with specific rites useful to give a child this new qualification being accepted among the other men and women in a peer relation. Before this, a child was considered an incapable individual (in a very broad sense) unable to correctly and wisely choice and thus requiring an external intervention for any correct decision.
Similarly a slave was considered as such because incapable (even if adult): slaves were considered like children. Even if slaves were member of the familia and for this not subjected to no-use arbitrary violence and abuses, they hadn't a qualification of humanitas. Slaves, lacking humanitas, were not able to have any idea of magnanimitas, aeqvitas, gravitas, prvdentia. They cannot achieve the Virtvus.
In brief, slavery is not only an exterior characteristics, but primarily it is an inner existential qualification. Slavery is a spiritual condition. One can be subjected to any kind of injustice being and remaining however a free man or woman. Viceversa, one totally subjected to any kind of physical pushes, instincts or urges may be apparently a free man/woman, but foundamentally a slave. To a free man's/woman's eyes, he/she seems to be like a whimsical kid or a foolish silly man/woman trapped into a chaotic tangle.
Seneca provides us with an interesting definition of "slave":
Sciet pro patria pugnandum esse, dissuadebit timor; sciet pro amicis desudandum esse ad extremum usque sudorem, sed deliciae vetabunt; sciet in uxore gravissimum esse genus iniuriae paelicem, sed illum libido in contraria inpinget. (Seneca Epist. 95 Liber XV)
"A man may know that he should fight for his country, but fear will dissuade him. A man may know that he should sweat forth his last drop of energy on behalf of his friends, but luxury will forbid. A man may know that keeping a mistress is the worst kind of insult to his wife, but lust will drive him in the opposite direction."
It also true the sentence of the Emperor Adrian according to whom slavery will never disappear: it will just change its name. All this clearly evidences how important is this issue also in our present times.
Freedom and slavery have not to be considered as something "given", but real freedom has to be achieved and maintained in the everyday praxes thanks to inner personal discipline, Virtvs towards mankind and Pietas towards the Immortals.