Plato, Letters 354b

εἴη, μεταβαλεῖν. δυνατὸν δέ, ὡς ἔδειξεν ἔργῳ σοφὸς ἀνὴρ καὶ ἀγαθὸς Λυκοῦργος, ὃς ἰδὼν τὸ τῶν οἰκείων γένος ἐν Ἄργει καὶ Μεσσήνῃ ἐκ βασιλέων εἰς τυράννων δύναμιν ἀφικομένους καὶ διαφθείραντας ἑαυτούς τε καὶ τὴν πόλιν ἑκατέρους ἑκατέραν, δείσας περὶ τῆς αὑτοῦ πόλεως ἅμα καὶ γένους, φάρμακον ἐπήνεγκεν τὴν τῶν γερόντων ἀρχὴν καὶ τὸν τῶν ἐφόρων δεσμὸν τῆς βασιλικῆς ἀρχῆς σωτήριον, ὥστε γενεὰς τοσαύτας ἤδη μετʼ εὐκλείας σῴζεσθαι, νόμος

That this is possible has been actually proved by that wise and good man Lycurgus ; for when he saw that the family of his kinsmen in Argos and in Messene had in both cases destroyed both themselves and their city by advancing from kingship to despotic power, he was alarmed about his own city as well as his own family, and as a remedy he introduced the authority of the Elders and of the Ephors to serve as a bond of safety for the kingly power ; and because of this they have already been kept safe