Symplegades

The Symplegades (/sɪmˈplɛɡədiːz/; Greek:Συμπληγάδες, Symplēgádes) or Clashing Rocks, also known as the Cyanean Rocks, were, according to Greek mythology, a pair of rocks at the Bosphorus that clashed together when somebody went through. They were defeated by Jason and the Argonauts, who would have been lost and killed by the rocks except for Phineus' advice. Jason let a dove fly between the rocks; it lost only its tail feathers. The Argonauts rowed mightily to get through and lost only part of the stern ornament. After that, the Symplegades stopped moving permanently.