Symplegades
In
Greek mythology, the
Sympleglades were a pair of rocks at the
Hellespont 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.
The Romans called them cyaneae insulae.
Apollonius Rhodius. Argonautica II, 317-340, 549-610