Bosporus

Bosporus (Bogazici) is a strait, which separates the European part of Istanbul from the Asian part by uniting the Marmara Sea with the Black Sea. There are two bridges across the strait: Bogazici (Bosporus I) Bridge (1,074 m; completed in 1973) and the Fatih Sultan Mehmed (Bosporus II) Bridge (1,090 m, completed in 1988). Having a strategic importance for the defense of Istanbul, Ottoman sultans have constructed two castles on both sides of the strait (Anadoluhisari, Rumelihisari).

The strategic importance of the straits is such that a number of international treaties have been agreed to control vessels using the waters, the current treaty in force is the Montreux Convention Regarding the Regime of the Turkish Straits (1936).