Plutarch, De Iside et Osiride 9

οἱ δὲ βασιλεῖς ἀπεδείκνυντο μὲν ἐκ τῶν ἱερέων ἢ τῶν μαχίμων, τοῦ μὲν διʼ ἀνδρείαν τοῦ δὲ διὰ σοφίαν γένους ἀξίωμα καὶ τιμὴν ἔχοντος. ὁ δʼ ἐκ μαχίμων ἀποδεδειγμένος εὐθὺς ἐγίγνετο τῶν ἱερέων καὶ μετεῖχε τῆς φιλοσοφίας, ἐπικεκρυμμένης τὰ πολλὰ μύθοις καὶ λόγοις ἀμυδρὰς ἐμφάσεις τῆς ἀληθείας καὶ διαφάσεις ἔχουσιν, ὥσπερ ἀμέλει καὶ παραδηλοῦσιν αὐτοὶ πρὸ τῶν ἱερῶν τὰς σφίγγας ἐπιεικῶς ἱστάντες, ὡς αἰνιγματώδη σοφίαν τῆς θεολογίας αὐτῶν ἐχούσης. τὸ δʼ ἐν Σάι τῆς Ἀθηνᾶς, ἣν καὶ Ἶσιν νομίζουσιν, ἕδος ἐπιγραφὴν εἶχε τοιαύτην ἐγώ εἰμι πᾶν τὸ γεγονὸς καὶ ὂν καὶ ἐσόμενον καὶ τὸν ἐμὸν πέπλον οὐδείς πω θνητὸς ἀπεκάλυψεν ἔτι δὲ τῶν πολλῶν νομιζόντων ἴδιον παρʼ Αἰγυπτίοις ὄνομα τοῦ Διὸς εἶναι τὸν Ἀμοῦν (ὃ παράγοντες ἡμεῖς Ἄμμωνα λέγομεν), Μανεθὼς μὲν ὁ Σεβεννύτης τὸ κεκρυμμένον οἴεται καὶ τὴν κρύψιν ὑπὸ ταύτης δηλοῦσθαι τῆς φωνῆς· Ἑκαταῖος δʼ ὁ Ἀβδηρίτης φησὶ τούτῳ καὶ πρὸς ἀλλήλους τῷ ῥήματι χρῆσθαι τοὺς Αἰγυπτίους, ὅταν τινὰ προσκαλῶνται· προσκλητικὴν γὰρ εἶναι τὴν φωνήν. διὸ τὸν πρῶτον θεόν, ὃν τῷ παντὶ τὸν αὐτὸν νομίζουσιν, ὡς ἀφανῆ καὶ κεκρυμμένον ὄντα προσκαλούμενοι καὶ παρακαλοῦντες ἐμφανῆ γενέσθαι καὶ δῆλον αὐτοῖς, Ἀμοῦν λέγουσιν. ἡ μὲν οὖν εὐλάβεια τῆς περὶ τὰ θεῖα σοφίας Αἰγυπτίων τοσαύτη ἦν.

The kings were appointed from the priests or from the military class, since the military class had eminence and honour because of valour, and the priests because of wisdom. But he who was appointed from the military class was at once made one of the priests and a participant in their philosophy, which, for the most part, is veiled in myths and in words containing dim reflexions and adumbrations of the truth, as they themselves intimate beyond question by appropriately placing sphinxes before their shrines to indicate that their religious teaching has in it an enigmatical sort of wisdom. In Saïs the statue of Athena, whom they believe to be Isis, bore the inscription: I am all that has been, and is, and shall be, and my robe no mortal has yet uncovered. Moreover, most people believe that Amoun is the name given to Zeus in the land of the Egyptians, a name which we, with a slight alteration, pronounce Ammon. But Manetho of Sebennytus thinks that the meaning concealed or concealment lies in this word. Hecataeus of Abdera, however, says that the Egyptians use this expression one to another whenever they call to anyone, for the word is a form of address. When they, therefore, address the supreme god, whom they believe to be the same as the Universe, as if he were invisible and concealed, and implore him to make himself visible and manifest to them, they use the word Amoun; so great, then, was the circumspection of the Egyptians in their wisdom touching all that had to do wTith the gods.