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