Passage 7.27.2
κατὰ δὲ τὴν ὁδὸν ἐς αὐτὴν τὴν πόλιν ἐστὶν Ἀθηνᾶς λίθου μὲν ἐπιχωρίου ναός, ἐλέφαντος δὲ τὸ ἄγαλμα καὶ χρυσοῦ· Φειδίαν δὲ εἶναι τὸν εἰργασμένον φασὶ πρότερον ἔτι ἢ ἐν τῇ ἀκροπόλει τε αὐτὸν τῇ Ἀθηναίων καὶ ἐν Πλαταιαῖς ποιῆσαι τῆς Ἀθηνᾶς τὰ ἀγάλματα. λέγουσι δὲ οἱ Πελληνεῖς καὶ ἄδυτον τῆς Ἀθηνᾶς καθήκειν ἐς βάθος τῆς γῆς, εἶναι δὲ τὸ ἄδυτον τοῦτο ὑπὸ τοῦ ἀγάλματος τῷ βάθρῳ, καὶ τὸν ἀέρα ἐκ τοῦ ἀδύτου νότιόν τε εἶναι καὶ διʼ αὐτὸ τῷ ἐλέφαντι ἐπιτήδειον.
On the road leading into the city itself is a temple to Athena, built from the local stone, but the statue is of ivory and gold. They say Phidias crafted this image even earlier than the statues of Athena he made on the Acropolis in Athens and at Plataea. The Pelleneans also say that a sanctuary chamber of Athena extends downward beneath the earth, situated beneath the statue's pedestal, and that the air from this underground chamber is moist and thereby beneficial to the ivory.