Ionian Sea, an arm of the Mediterranean Sea. It is bounded on the north by the Strait of Otranto, which connects it with the Adriatic Sea; on the east by Greece; and on the west by Sicily, the Italian mainland, and the Strait of Messina, which connects it with the Tyrrhenian Sea. The Corinth Canal across the Isthmus of Corinth in Greece links the Ionian Sea to the Aegean Sea. The Ionian Sea's greatest width is about 400 miles (640 km). Principal ports are Patras and Corfu (Greece), and Catania and Syracuse (Sicily).