Bosphorous
The strait of Istanbul, called the Bosporus, is a narrow strait connecting the Black Sea with the Mediterranean. The city of Istanbul bridges the Bosphorus, making it the only city in the world located on two continents. The strait separates the Asian continent from that of the European, running 30 kilometers long. The Bosphorus has a maximum width of 3.7 kilometers (2.3 miles), and a minimum width of 750 meters (2,450 feet). At its narrowest point, it is guarded by two castles: Anadolu Hisari built in 1390 on the Asian side, and Rumeli Hisari built in 1452 on the European side. Along both shores, there are waterfront mansions called yalıs, built from wood and traditionally used as summer houses by the Ottomans. Two bridges were built on the Bosphorus, the first in 1973 and the second in 1988, and a recent addition of a rail tunnel under the water has been made in 2013.