Since the siege of Troy, the Turkish Straits between the Dardanelles and the Northern end of the Bosphorus have been of vital strategic importance. The water has been both a source of prosperity and the cause of political battles for Istanbul. Tom de Waal takes a journey up the Bosphorus and talks to writers Orhan Pamuk and Elif Shafak, Professors Gun Kut and Edhem Eldem, and Captains Rajiv Kumar and Mete Kocar to present a portrait of Istanbul as seen from its seaway.