Plato, Laws 760c

ἐκ τῶν νέων, μὴ ἔλαττον ἢ πέντε καὶ εἴκοσιν ἔτη γεγονότας, μὴ πλεῖον δὲ ἢ τριάκοντα. τούτοις δὲ διακληρωθήτω τὰ μόρια τῆς χώρας κατὰ μῆνα ἕκαστα ἑκάστοις, ὅπως ἂν πάσης τῆς χώρας ἔμπειροί τε καὶ ἐπιστήμονες γίγνωνται πάντες. δύο δʼ ἔτη τὴν ἀρχὴν καὶ τὴν φρουρὰν γίγνεσθαι φρουροῖς τε καὶ ἄρχουσιν. ὅπως δʼ ἂν τὸ πρῶτον λάχωσιν τὰ μέρη, τοὺς τῆς χώρας τόπους, μεταλλάττοντας ἀεὶ τὸν ἑξῆς τόπον

young men from his own tribe of an age neither under 25 nor over 30. To these groups of twelve the twelve portions of the country shall be assigned, one to each in rotation for a month at a time, so that all of them may gain experience and knowledge of all parts of the country. The period of office and of service for guards and officers shall be two years. From the portion in which they are stationed first by the lot they shall pass on month by month to the next district, under the leadership of the phrourarchs, in a direction from left to right,—