Passage 2.33.1
νῆσοι δέ εἰσι Τροιζηνίοις μία μὲν πλησίον τῆς ἠπείρου, καὶ διαβῆναι ποσὶν ἐς αὐτὴν ἔστιν· αὕτη Σφαιρία ὀνομαζομένη πρότερον Ἱερὰ διʼ αἰτίαν ἐκλήθη τοιαύτην. ἔστιν ἐν αὐτῇ Σφαίρου μνῆμα· Πέλοπος δὲ ἡνίοχον εἶναι λέγουσι τὸν Σφαῖρον. τούτῳ κατὰ δή τι ἐξ Ἀθηνᾶς ὄνειρον κομίζουσα Αἴθρα ἐς χοὰς διέβαινεν ἐς τὴν νῆσον, διαβάσῃ δὲ ἐνταῦθα λέγεται Ποσειδῶνα μιχθῆναι. ἱδρύσατο μὲν διὰ τοῦτο Αἴθρα ναὸν ἐνταῦθα Ἀθηνᾶς Ἀπατουρίας καὶ Ἱερὰν ἀντὶ Σφαιρίας ὠνόμασε τὴν νῆσον· κατεστήσατο δὲ καὶ ταῖς Τροιζηνίων παρθένοις ἀνατιθέναι πρὸ γάμου τὴν ζώνην τῇ Ἀθηνᾷ τῇ Ἀπατουρίᾳ.
The Troezenians possess islands, of which one lies close to the mainland, and can even be reached on foot. This island, now called Sphairia, was previously named "Hiera" (Sacred) for the following reason. On it is found the tomb of Sphairos, who, they say, was once the charioteer of Pelops. It is said that Aithra, following a dream sent by Athena, crossed over onto the island in order to offer libations to his grave; once there, Poseidon is said to have united with her. Because of this encounter, Aithra established there a temple to Athena Apatouria, renaming the island Hiera instead of Sphairia. She also established the custom that the Troezenian maidens dedicate their girdles to Athena Apatouria before marriage.