There are ferry routes between Patras and Igoumenitsa, Greece, and Brindisi and Ancona, Italy, that cross the east and north of the Ionian Sea, and from Piraeus westward. Calypso Deep, the deepest point in the Mediterranean at −5,267 m (−17,280 ft), is located in the Ionian Sea, at 36°34′N 21°8′E. The sea is one of the most seismically active areas in the world.
The name Ionian comes from Greek language Ἰόνιον (πέλαγος). Its etymology is unknown. Ancient Greek writers, especially Aeschylus, linked it to the myth of Io. In Ancient Greek the adjective Ionios (Ἰόνιος) was used as an epithet for the sea because Io swam across it. There were also narratives about other eponymic legendary figures; according to one version, Ionius was a son of Adrias (eponymic for the Adriatic Sea); according to another, Ionius was a son of Dyrrhachus, eponymic for the ancient Illyrian city of Dyrrhachium (modern Durrës in Albania). When Dyrrhachus was attacked by his own brothers, Heracles, who was passing through the area, came to his aid, but in the fight the hero killed his ally's son by mistake. The corpse was cast into the sea, which thereafter was called the Ionian Sea.