Passage 10.18.6
ἔστιν ἐνταῦθα καὶ ἄθλων τῶν Ἡρακλέους τὸ ἐς τὴν ὕδραν, ἀνάθημά τε ὁμοῦ Τισαγόρου καὶ τέχνη, σιδήρου καὶ ἡ ὕδρα καὶ ὁ Ἡρακλῆς. σιδήρου δὲ ἐργασίαν τὴν ἐπὶ ἀγάλμασι χαλεπωτάτην καὶ πόνου συμβέβηκεν εἶναι πλείστου· θαύματος μὲν δὴ καὶ τοῦ Τισαγόρου τὸ ἔργον, ὅστις δὴ ὁ Τισαγόρας, θαύματος δὲ οὐκ ἐλαχίστου καὶ ἐν Περγάμῳ λέοντός τε καὶ ὑὸς ἀγρίου κεφαλαί, σιδήρου καὶ αὗται· Διονύσῳ δὲ ἀναθήματα σφᾶς ἐποιήσαντο.
Here too is represented the labor of Heracles concerning the Hydra, an offering and work wrought by Tisagoras, both the Hydra and Heracles himself being of iron. Among statues, iron workmanship is found to be the most difficult and involves the greatest labor. Indeed, the work of this Tisagoras is marvelous; and not least marvelous are two iron heads, one of a lion and one of a wild boar, at Pergamus. These heads were dedicated as votive offerings to Dionysus.