Bosphorus is one of the two straits separating two continents: Asia and Europe; and connects two seas : the Black Sea and The Marmara Sea. Bosphorus and its shores are the most beautiful part of Istanbul. Gyllius eloquently describes it as "The first creator of Byzantium, greater and more important than Byzas, the legendary founder of the city".

The strait is about 30 km long and from 670 meters wide at the most narrow part very close to the Rumeli Castle, over three and half kilometers at its widest part. The average deepness of the strait is 50-60 meters and very close to the Fatih Bridge its deepness reaches to 120 meters. The surface current of the water is 3 to 5 km per hour from Black Sea towards Marmara Sea. And about 35 - 40 meters below the surface a subcurrent exists.