Plato, Letters 359a

ἔχω σοί τε καὶ τοῖς οἰκισταῖς, ὃ εἰπόντος μὲν ἐμοῦ, φησὶν Ἡσίοδος, δόξαι ἂν εἶναι φαῦλον, χαλεπὸν δὲ νοῆσαι. εἰ γὰρ οἷόν τε ὑπὸ νόμων θέσεως καὶ ὧντινων εὖ ποτε πολιτείαν κατασκευασθῆναι ἄνευ τοῦ εἶναί τι κύριον ἐπιμελούμενον ἐν τῇ πόλει τῆς καθʼ ἡμέραν διαίτης, ὅπως ἂν ᾖ σώφρων τε καὶ ἀνδρικὴ δούλων τε καὶ ἐλευθέρων, οὐκ ὀρθῶς διανοοῦνται. τοῦτο δʼ αὖ, εἰ μέν εἰσιν ἤδη ἄνδρες ἄξιοι

I am able, however, to give you and the settlers advice which may seem to be, as Hesiod says, Trivial when uttered by me, but hard to be understanded. For they are mistaken if they believe that a constitution could ever be well established by any kind of legislation whatsoever without the existence of some authority in the State which supervises the daily life both of slaves and freemen, to see that it is both temperate and manly. And this condition might be secured if you already possess men who are worthy of such authority.