Mythology & Beliefs: Symplegades In Greek and Roman Mythology, Symplegades were clashing rocks at entrance to Black Sea; Argo passed through, causing them to become forever fixed.
Symplegades in Wikipedia
The Symplegades (pronounced /sɪmˈplɛɡədiːz/; Greek:
Συμπληγάδες, Sumplēgades) or Clashing Rocks, also known as the
Cyanean Rocks, were, according to Greek mythology, a pair of
rocks at the Bosphorus that clashed together randomly. They
were defeated by Jason and the Argonauts, who would have been
lost and killed by the rocks except for Phineas' 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...