The Symplegades are the "Clashing Rocks" through which the Argo had to pass in order to enter the Hellespont. They moved randomly about in the sea, crashing together and crushing ships between them. No humans had ever passed safely through them. Acting on the advice of the seer Phineus, Jason let a dove fly through the rocks to see if the passage was safe; the dove passed through, losing only its tail feathers as the rocks crashed together behind it. Jason and his Argonauts then rowed mightily through the passage, and the Argo made the hazardous trip safely, losing only a piece of her stern ornament. After the Argo's successful journey, the Symplegades stopped moving and became firmly rooted in the sea. The Romans called them Cyaneae insulae.