Plato, Laws 742a

ἐξεῖναι χρυσὸν μηδὲ ἄργυρον κεκτῆσθαι μηδένα μηδενὶ ἰδιώτῃ, νόμισμα δὲ ἕνεκα ἀλλαγῆς τῆς καθʼ ἡμέραν, ἣν δημιουργοῖς τε ἀλλάττεσθαι σχεδὸν ἀναγκαῖον, καὶ πᾶσιν ὁπόσων χρεία τῶν τοιούτων μισθοὺς μισθωτοῖς, δούλοις καὶ ἐποίκοις, ἀποτίνειν. ὧν ἕνεκά φαμεν τὸ νόμισμα κτητέον αὐτοῖς μὲν ἔντιμον, τοῖς δὲ ἄλλοις ἀνθρώποις ἀδόκιμον· κοινὸν δὲ Ἑλληνικὸν νόμισμα ἕνεκά τε στρατειῶν καὶ ἀποδημιῶν εἰς τοὺς ἄλλους ἀνθρώπους, οἷον πρεσβειῶν ἢ καί

there follows also a law which forbids any private person to possess any gold or silver, only coin for purposes of such daily exchange as it is almost necessary for craftsmen to make use of, and all who need such things in paying wages to hirelings, whether slaves or immigrants. For these reasons we say that our people should possess coined money which is legal tender among themselves, but vaIueless elsewhere. As regards the universal Hellenic coinage,—for the sake of expeditions and foreign visits, as well as of embassies or any other missions necessary for the State, if there be need to send someone abroad,—for such objects as these it is necessary that the State should always possess Hellenic money.