"The strait that surpasses all straits…The Bosporus with one key opens and closes two worlds, two seas."
Strolling Through Istanbul, John Freely (2000)
The Bosporus forms a natural border between the European and the Asian part of Istanbul, while also connecting the Black Sea with the Sea of Marmara. It is 32 km long and one of the world's narrowest strait as well as one of the most significant shipping routes. There is 24 hour traffic of cargo ships, container vessels, oil-tankers, sea-fishing boats and cruisers.
The density of maritime traffic in Bosporus has increased eleven-fold since the beginning of the 20th century. In recent years the Bosporus has also become an important oil transit route, which poses a significant environmental threat. Approximately every ten minutes a ship is passing by. "1.5 million people travel daily through the straits." (Today's Zaman, 24 June 2008).
Two bridges cross the Bosporus: the first was completed in 1973; the second, Fatih Sultan Mehmet Bridge, was completed in 1988. Both bridges are over 1 km long. Plans for a third road bridge have already been approved by the Ministry of Transportation.
Another major construction project is the Marmaray Railway line which will connect the European and the Asian side under the Bosporus by train. The tunnel will connect the historic Eminonu to Uskudar. In total the train line will be over 76 km long of which 13.6 km will be underground. Work started in May 2004 and is expected to be completed in 2012.