This article is about the strait; Bosphorus is also a university in Turkey.
The Bosporus or Bosphorus (Turkish Boğaziçi or İstanbul Boğazı) is a strait that separates the European part (Rumeli) of Turkey from its Asian part (Anadolu), connecting the Sea of Marmara (Marmara Denizi) with the Black Sea (Karadeniz). It is 30 km long, with a maximum width of 3,700 meters at the northern entrance, and a minimum width of 750 meters between Anadoluhisarı and Rumelihisarı. The depth varies from 36 to 124 meters in midstrem.
The shores of the strait are heavily populated as the city of Istanbul (population at least 11 million) straddles it.
Two bridges cross the Bosporus Strait. The first, Bogazici (Bosporus I) bridge, is 1074 meters long and was completed in 1973. The second, Fatih Sultan Mehmed (Bosporus II) bridge, is 1090 meters long, and was completed in 1988 about five kilometers north of the first bridge.
Marmaray, a 13.7 kilometer-long rail tunnel is under construction and expected to be completed in 2008. Approximately 1,400 meters of the tunnel will run under the strait, at a depth of about 55 meters.
The ancient Greeks referred to this strait as the Thracian Bosporus, as they called the Strait of Kerch the Cimmerian Bosporus. Increasing the chances of confusion, they also called a land area near these two straits by the same name: the Thracian Chersonesus, which is known today as Gallipoli, and the Cimmerian Chersonesus, known today as the Crimea.
Due to the importance of the strait for the defense of Istanbul, the Ottoman sultans constructed a fortification on each side of it, Anadoluhisari (1393) and Rumelihisari (1451). Its strategic importance remains high: several international treaties have governed vessels using the waters. including the Montreux Convention Regarding the Regime of the Turkish Straits, signed in 1936.
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