Istanbul is the modern name used for the city called Constantinople in Assassin's Creed Revelations.
The game is set primarily in Constantinople in 1511, during the Ottoman period. Modern historical usage generally calls the city Istanbul, while Constantinople was the name used in the game's period and remains important to its historical context. The city occupies the meeting point of Europe and Asia around the Bosporus.
Ezio travels there to find keys connected with Altaïr's legacy and becomes involved with the Ottoman Assassins. The game includes districts such as Galata, Constantine, Bayezid, and Imperial, along with extensive rooftop movement and underground passages.
Istanbul is not the game's usual period name, so answers such as Athens or Alexandria are incorrect. Bursa was an Ottoman capital before Constantinople, but it is not the principal city in Revelations.