Plato, Laws 767b

δικαστὰς ὡς ἄρχοντας, λέγωμεν τίνες ἂν εἶεν πρέποντες καὶ τίνων ἄρα δικασταὶ καὶ πόσοι ἐφʼ ἕκαστον. κυριώτατον μὲν τοίνυν ἔστω δικαστήριον ὅπερ ἂν αὐτοὶ ἑαυτοῖς ἀποφήνωσιν ἕκαστοι, κοινῇ τινας ἑλόμενοι· δύο δὴ τῶν λοιπῶν ἔστω κριτήρια, τὸ μὲν ὅταν τίς τινα ἰδιώτην ἰδιώτης, ἐπαιτιώμενος ἀδικεῖν αὐτόν, ἄγων εἰς δίκην βούληται διακριθῆναι, τὸ δʼ ὁπόταν τὸ δημόσιον ὑπό τινος τῶν πολιτῶν ἡγῆταί

Assuming then that the judges are officials, let us declare who will make suitable judges, and of what matters, and how many shall deal with each case. The most elementary form of court is that which the two parties arrange for themselves, choosing judges by mutual agreement; of the rest, there shall be two forms of trial,—the one when a private person accuses a private person of injuring him and desires to gain a verdict by bringing him to trial, and the other when a person believes that the State is being injured by one of the citizens