Bosporus bŏs´pərəs [key] or Bosphorus –pərəs [key] [Gr.,=ox ford, in reference to the story of Io ], Turk. Boğaziçi, strait, c.20 mi (30 km) long and c.2,100 ft (640 m) wide at its narrowest, separating European from Asian Turkey and joining the Black Sea with the Sea of Marmara . İstanbul straddles the Bosporus. At its narrowest point stand two famous castles: Anadolu Hisar (1390) on the Asian side and Rumeli Hisar (1452) on the European side. With the Dardanelles , the Bosporus connects the Black Sea with the Mediterranean; it is thought to have been a dry riverbed as recently as 7,600 years ago. The July 15th Martyrs Bridge (formerly the Bosporus Bridge; a suspension bridge) opened in 1973. A second suspension bridge, the Fatih Sultan Mehmet Bridge, was completed in 1988, a railroad tunnel under the strait opened in 2013, and a third bridge, the Yavuz Sultan Selim Bridge, a hybrid cable-stayed suspension bridge, opened in 2016; all are in İstanbul. In 2011 the Turkish government proposed building a canal parallel to the Bosporus to reduce the shipping congestion in the strait.

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