In Greek mythology, Aegeus warned Theseus to watch the sails on his return from Crete.
Aegeus was the king of Athens and Theseus’s father in the principal tradition. Before Theseus sailed to confront the Minotaur, Aegeus asked him to replace the ship’s black sails with white ones if he survived. The change would serve as a signal that Theseus was returning safely.
Theseus defeated the Minotaur and escaped, but he forgot to change the sails. Seeing the black sails from the coast, Aegeus believed his son had died and threw himself into the sea. The sea was subsequently associated with his name in Greek geography.
The episode explains the tragic ending of Theseus’s return and gives a mythological origin for the name Aegean Sea. Different ancient accounts vary in smaller details, but Aegeus’s role as the anxious father awaiting the signal is a stable part of the story.