In Book XII of the Odyssey, Circe warns Odysseus about the terrible six-headed monster Skylla who will take six of his men as their ship passes her lair. Representations of Skylla are comparatively rare in ancient art, her first appearance being on an Etruscan ivory box from Chiusi of circa 600 B.C. She appears in Greek art in the mid 5th century, but her image (upper body of a woman, lower body fish-like) differs considerably from Homer's description. Skylla holding a rock can be found on the helmet of Athena on coins minted at Thurii and elsewhere. For a recent discussion by Buitron see pp. 136-153 in The Odyssey and Ancient Art, An Epic in Word and Image.