The Bosphorus or Bosporus, also known as Istanbul Strait, (Turkish: Boğaziçi, İstanbul Boğazı or just Boğaz) (Greek: Βόσπορος) (English also: Bosphorus) is a strait that forms the boundary between the European part (Rumeli) of Turkey and its Asian part (Anadolu). The world's narrowest strait used for international navigation, it connects the Black Sea with the Sea of Marmara (which is connected by the Dardanelles to the Aegean Sea, and thereby to the Mediterranean Sea).
The name, means ox passage or cow-ford from the Greek word Bosphorus (Βόσπορος), it is associated with a Greek myth about Io's travels after Zeus turned her into an ox for her protection.
It is also said in myth that floating rocks once crushed any ship that attempted passage of the Bosporus until the hero Jason obtained passage by trickery, whereupon the rocks became fixed, and Greek access to the Black Sea was opened.
Two bridges cross the Istanbul Strait. The first, Bogazici (Bosphorus I) bridge, is 1074 meters long and was completed in 1973. The second, Fatih Sultan Mehmet (Bosphorus II) bridge, is 1090 meters long, and was completed in 1988 about five kilometers north of the first bridge. A third road bridge is also being planned.