The Bosporus is the strait between the Black Sea and the Sea of Marmara crossed by Istanbul’s bridges.
It runs through Istanbul and is one of the world’s best-known urban waterways. The strait forms part of the boundary between the European and Asian sides of the city, making Istanbul a transcontinental metropolis. Its northern end opens into the Black Sea, while its southern end leads through the Sea of Marmara toward the Dardanelles and the Aegean Sea.
Several major bridges cross the Bosporus, including the 15 July Martyrs Bridge, the Fatih Sultan Mehmet Bridge, and the Yavuz Sultan Selim Bridge. The Eurasia Tunnel also carries road traffic beneath the waterway.
The Bosporus is not the Dardanelles: the Dardanelles lies farther southwest and connects the Sea of Marmara with the Aegean Sea. Together, the two straits provide the maritime route between the Black Sea and the Mediterranean.