Plato, Laws 765c

τοὺς κριτὰς ἀποδιδοὺς ὁ λαχὼν τὴν κρίσιν. μετὰ δὲ ταῦτα χρεὼν ἀγωνίας ἀθλοθέτας αἱρεῖσθαι τῆς περὶ τὰ γυμνάσια ἵππων τε καὶ ἀνθρώπων ἐκ τῶν τρίτων τε καὶ ἔτι τῶν δευτέρων τιμημάτων· εἰς δὲ τὴν αἵρεσιν ἔστω μὲν ἐπάναγκες τοῖς τρισὶν πορεύεσθαι τιμήμασι, τὸ σμικρότατον δὲ ἀζήμιον ἀφείσθω. τρεῖς δʼ ἔστωσαν οἱ λαχόντες, τῶν προχειροτονηθέντων μὲν εἴκοσι, λαχόντων δὲ ἐκ τῶν εἴκοσι τριῶν, οὓς ἂν καὶ ψῆφος ἡ τῶν δοκιμαζόντων δοκιμάσῃ· ἐὰν

Next it is proper to choose umpires for the athletic contests of horses and men from among the third and the second property-classes: this election it shall be compulsory for the first three classes to attend, but the lowest class shall be exempt from fines for non-attendance. Three shall be appointed: twenty having been first selected by show of hand, three out of the twenty shall be chosen by lot; and they shall be subject also to the approval of the scrutineers.