Plato, Laws 771b

τε καὶ ἔχει τομὰς προσφόρους ὅ τε ὅλος ἅμα καὶ ὁ κατὰ φυλάς, ὃ δὴ τοῦ παντὸς ἔθεμεν δωδεκατημόριον, ἓν καὶ εἴκοσιν εἰκοσάκις ὀρθότατα φύν. ἔχει δὲ διανομὰς δώδεκα μὲν ὁ πᾶς ἀριθμὸς ἡμῖν, δώδεκα δὲ καὶ ὁ τῆς φυλῆς· ἑκάστην δὴ τὴν μοῖραν διανοεῖσθαι χρεὼν ὡς οὖσαν ἱεράν, θεοῦ δῶρον, ἑπομένην τοῖς μησὶν καὶ τῇ τοῦ παντὸς περιόδῳ. διὸ καὶ πᾶσαν πόλιν ἄγει μὲν τὸ σύμφυτον ἱεροῦν αὐτάς, ἄλλοι δὲ ἄλλων ἴσως ὀρθότερον ἐνείμαντό τε καὶ εὐτυχέστερον ἐθείωσαν τὴν

both as a whole and when divided up into tribes: the tribal number is, as we said, a twelfth part of the whole number, being in its nature precisely 20 X 21. Our whole number has twelve subdivisions, and the tribal number also has twelve; and each such portion must be regarded as a sacred gift of God, conformed to the months and to the revolution of the universe. Wherefore also every State is guided by native instinct to hold them sacred, although some men possibly have made their divisions more correctly than others, or have consecrated them