Constantinople serves as the Assassin Brotherhood's headquarters in Assassin's Creed Revelations.
The game follows Ezio Auditore as he travels to Constantinople, the capital of the Byzantine Empire, during the early sixteenth century. Ezio investigates the Masyaf Keys and searches for knowledge connected to Altaïr Ibn-La'Ahad, linking the two protagonists' stories.
Constantinople is divided into districts controlled by the Templars. Ezio can liberate districts, recruit local Assassins, and defend them against counterattacks. The city includes districts such as Galata, Constantine, and Imperial, along with landmarks including Hagia Sophia and the Grand Bazaar.
The modern city is now called Istanbul, but Constantinople is the historical name used for the game's setting and the canonical answer to this question. Revelations also returns to Masyaf and includes a substantial modern-day storyline involving Desmond Miles.