The Bosporus divides Istanbul’s European and Asian sides and links the Black Sea with the Sea of Marmara.
The strait is about 31 kilometres long and varies considerably in width. Istanbul occupies both shores, making the Bosporus one of the world’s most prominent urban waterways. Two major suspension bridges and the Eurasia Tunnel cross beneath or above it.
The Bosporus forms part of the Turkish Straits system. Southward, ships continue through the Sea of Marmara and the Dardanelles to reach the Aegean Sea and the Mediterranean. The Dardanelles is therefore a separate strait, not another name for the Bosporus.
Its name comes from the Greek Bosporos, traditionally interpreted as “ox passage.” Ancient Greek mythology associated the name with Io, who was transformed into a cow. Modern shipping, ferries and dense shoreline settlement make the waterway both strategically important and highly visible.