Scylla was a monster that lived on one side of a narrow channel of water, opposite her counterpart Charybdis.
Scylla was a beautiful naiad who was claimed by Poseidon, but the jealous Amphitrite turned her into a monster by poisoning the water of the spring where Scylla would bathe.
In Homer's Odyssey XII, Odysseus is advised by Circe to sail closer to Scylla, for Charybdis could drown his whole ship: "Hug Scylla's crag—sail on past her—top speed! Better by far to lose six men and keep your ship than lose your entire crew."[