Istanbul is a metropolis of 15 million people and occupies both sides of the entrance to the narrow, 32-kilometer (20-mile) long Bosphorus Strait connecting the Mediterranean and Sea of Marmara to the south and the Black Sea to the north. From its founding as Byzantium by the Greeks in 600 B.C., this strategically located city has been a focus of maritime trade and commerce as well as an outpost and threshold for cultural exchange and conflict between Europe and Asia. The modern city's layout and architecture show the influences of both the Roman-Byzantine era when it became Constantinople, the world's first Christian capital, as well as that of the conquering Ottoman Turks, from 1453, when it became the seat of the world's largest Muslim empire. Today, Istanbul is Turkey's economic capital and home to nearly half the country's wealth.
Sketch of the basic structure: