The Dardanelles and Bosporus Passages
The dividing line between Europe and Asia, the link up between the
Mediterranean and the Back Sea, the Bosporus is an ancient valley along
a fractured tectonic line. From the Mediterranean Ocean, it runs through
the Dardanelles passage to reach the Sea of Marmara, a small interior
sea. Then, the narrow Bosporus passage (1 km at its narrowest point)
goes through Istanbul to reach the Black Sea.