Istanbul is a rare place. It’s the only city to straddle Europe and the Middle East; the Turkish metropolis is simultaneously an Asian and a European city. This geography helps explain why it was once the capital of the Eastern Roman Empire, also known as the Byzantine Empire, when the city was called Constantinople, and then later why it became the power base of the Ottoman sultans, whose influence stretched into Africa and the Arab world. 

But exactly when did Constantinople change its name to Istanbul?

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