Passage 2.13.7
ὄπισθεν δὲ τῆς ἀγορᾶς ἐστιν οἶκος ὀνομαζόμενος ὑπὸ Φλιασίων μαντικός. ἐς τοῦτον Ἀμφιάραος ἐλθὼν καὶ τὴν νύκτα ἐγκατακοιμηθεὶς μαντεύεσθαι τότε πρῶτον, ὡς οἱ Φλιάσιοί φασιν, ἤρξατο· τέως δὲ ἦν Ἀμφιάραος τῷ ἐκείνων λόγῳ ἰδιώτης τε καὶ οὐ μάντις. καὶ τὸ οἴκημα ἀπὸ τούτου συγκέκλεισται τὸν πάντα ἤδη χρόνον. οὐ πόρρω δέ ἐστιν ὁ καλούμενος Ὀμφαλός, Πελοποννήσου δὲ πάσης μέσον, εἰ δὴ τὰ ὄντα εἰρήκασιν. ἀπὸ δὲ τοῦ Ὀμφαλοῦ προελθοῦσι Διονύσου σφίσιν ἱερόν ἐστιν ἀρχαῖον, ἔστι δὲ καὶ Ἀπόλλωνος καὶ ἄλλο Ἴσιδος. τὸ μὲν δὴ ἄγαλμα τοῦ Διονύσου δῆλον πᾶσιν, ὡσαύτως δὲ καὶ τὸ τοῦ Ἀπόλλωνος· τὸ δὲ τῆς Ἴσιδος τοῖς ἱερεῦσι θεάσασθαι μόνον ἔστι.
Behind the marketplace is a building called by the Phliasians "the prophetic house." According to the Phliasians, it was into this house that Amphiaraus entered and, having lain down at night there to sleep, began for the first time to prophesy; before this event, they say, Amphiaraus had been merely an ordinary man and not yet a seer. Afterward, the building remained closed for all time. Not far away is a place called the Omphalos ("the navel"), reputed to be the center of the entire Peloponnese, assuming their statement is correct. Beyond the Omphalos, as one moves forward, lies an ancient sanctuary of Dionysus; there is also one of Apollo and another dedicated to Isis. The image of Dionysus is clearly visible to all, as likewise is that of Apollo. But the statue of Isis can be seen only by the priests.