Plato, Laws 758b

ἡμέραν ἄρχοντας ἄρχουσιν, φρουροῦντάς τε φρουροῦσιν διαδεχομένους ἀεὶ καὶ παραδιδόντας μηδέποτε λήγειν. πλῆθος δὲ οὐ δυνατὸν ὀξέως οὐδέποτε οὐδὲν τούτων πράττειν, ἀναγκαῖον δὲ τοὺς μὲν πολλοὺς τῶν βουλευτῶν ἐπὶ τὸν πλεῖστον τοῦ χρόνου ἐᾶν ἐπὶ τοῖς αὑτῶν ἰδίοισι μένοντας εὐθημονεῖσθαι τὰ κατὰ τὰς αὑτῶν οἰκήσεις, τὸ δὲ δωδέκατον μέρος αὐτῶν ἐπὶ δώδεκα μῆνας νείμαντας, ἓν ἐφʼ ἑνὶ παρέχειν αὐτοὺς

and guardians succeeding guardians, and being succeeded in turn, without a break. But since a crowd of men is incapable of ever performing any of these duties smartly, the bulk of the Councillors must necessarily be left to stay most of their time at their private business, to attend to their domestic affairs; and we must assign a twelfth part of them to each of the twelve months, to furnish guards in rotation, so as promptly to meet any person coming either from somewhere abroad or