Plato, Letters 335d

διὰ πάσης τῆς ἀρχῆς, μεγίστην δύναμιν ἔχων, ἐν ᾗ γενομένη φιλοσοφία τε καὶ δύναμις ὄντως ἐν ταὐτῷ διὰ πάντων ἀνθρώπων Ἑλλήνων τε καὶ βαρβάρων λάμψασʼ ἂν ἱκανῶς δόξαν παρέστησεν πᾶσιν τὴν ἀληθῆ, ὡς οὐκ ἄν ποτε γένοιτο εὐδαίμων οὔτε πόλις οὔτʼ ἀνὴρ οὐδείς, ὃς ἂν μὴ μετὰ φρονήσεως ὑπὸ δικαιοσύνῃ διαγάγῃ τὸν βίον, ἤτοι ἐν αὑτῷ κεκτημένος ἢ ὁσίων ἀνδρῶν ἀρχόντων ἐν ἤθεσιν τραφείς τε καὶ παιδευθεὶς

throughout all his empire; although if, in that empire, philosophy and power had really been united in the same person the radiance thereof would have shone through the whole world of Greeks and barbarians, and fully imbued them with the true conviction that no State nor any individual man can ever become happy unless he passes his life in subjection to justice combined with wisdom, whether it be that he possesses these virtues within himself or as the result of being reared and trained righteously under holy rulers in their ways.