Plato, Republic, book 1 548:

πόλιν φαίησ ἂν ἄδικον εἶναι καὶ ἄλλασ πόλεισ ἐπιχειρεῖν δουλοῦσθαι ἀδίκωσ καὶ καταδεδουλῶσθαι, πολλὰσ δὲ καὶ ὑφ’ ἑαυτῇ ἔχειν δουλωσαμένην;