"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 is one of the world's narrowest straits. It is also one of the most significant global shipping routes, with 24 hour traffic of cargo ships, container vessels, oil tankers, sea fishing boats and cruisers.
The volume of maritime traffic in the 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. A ship passes by approximately every ten minutes. "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 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 sides under the Bosporus by train. The tunnel will connect Uskudar with the historic Eminonu. In total, the rail 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.