Passage 9.23.1
Θηβαίοις δὲ πρὸ τῶν πυλῶν ἐστι τῶν Προιτίδων καὶ τὸ Ἰολάου καλούμενον γυμνάσιον καὶ στάδιον κατὰ ταὐτὰ τῷ τε ἐν Ὀλυμπίᾳ καὶ τῷ Ἐπιδαυρίων γῆς χῶμα· ἐνταῦθα δείκνυται καὶ ἡρῷον Ἰολάου. τελευτῆσαι δὲ ἐν Σαρδοῖ τόν τε Ἰόλαον αὐτὸν καὶ Ἀθηναίων καὶ Θεσπιέων τοὺς συνδιαβάντας ὁμολογοῦσι καὶ οἱ Θηβαῖοι.
Before the Proetidian Gate of the Thebans is located the gymnasium called "of Iolaus," and also a stadium similar in form to the one at Olympia and to the earthen one in the territory of Epidaurus. At this site is also shown the hero shrine of Iolaus. The Thebans themselves agree that Iolaus, along with the Athenians and Thespians who crossed over with him, met their end in Sardinia.