A.A. Long in The Literary Hub:
The chief constraint on personal freedom in ancient Greece and Rome was what Epictetus knew at first hand, the social practice and indignity of slavery. It was slavery, the condition of being literally owned and made to serve at another’s behest that gave ancient freedom its intensely positive value and emotional charge. Slaves’ bodily movements during their waking lives were strictly constrained by their masters’ wishes and by the menial functions they were required to perform. But slaves, like everyone else, had minds, and minds as well as bodies are subject to freedom and constraint. You can be externally free and internally a slave, controlled by psychological masters in the form of disabling desires and passions and cravings. Conversely, you could be outwardly obstructed or even in literal bondage but internally free from frustration and disharmony, so free in fact that you found yourself in charge of your own well-being, lacking little or nothing that you could not provide for yourself. The latter, in essence, is the freedom that Epictetus, the ancient Stoic philosopher, made the central theme of his teaching.
Stoic philosophy had originated in Greece at the end of the fourth century BC. Its founding fathers were eastern Mediterranean immigrants to Athens, which was no longer a vibrant democracy, as the city had been at the time of Socrates, but a client state of the kingdom of Macedonia. Loss of political autonomy was reflected in philosophy at Athens by an inward turn in the focus of ethics. Neither Stoicism nor Epicureanism, the other leading Hellenistic school, engaged strongly in political theory, as their predecessors Plato and Aristotle had done. The main focus of the younger philosophers’ societal attention was not politics and legislation but personal well-being and self-improvement. This inward turn is strikingly illustrated by the way Stoic thought from its beginning treated freedom and slavery as primarily ethical and psychological denominators rather than marks of social status. According to Zeno, the original head of the Stoic school, freedom is the exclusive prerogative of those who are wise, while inferior persons, who comprise the majority of people, are not only fools but also slaves.