Constantinople (Ottoman Turkish: قسطنطینیه), also known as Istanbul to its Turkish rulers, was the capital of the Ottoman Empire, situated on the eastern edge of Europe. During the Renaissance, it was one of Europe's largest, and wealthiest, cities. It consisted of four distinct districts; Constantin, Beyazid, Imperial, and Galata.
Around 1209, the city was visited by the then Grand Master of the Assassin Order, Altaïr Ibn-La'Ahad. During his time there, he hid five seals that, when brought together, would unlock the inner sanctum of the fortress of Masyaf.
During the Renaissance, at some point between 1501 and 1507, the Doge of Venice, and Sultan Bayezid II, sought to ally their considerable naval powers through a free trade treaty. However, the Templars were wary of any peace between the two, and became intent on interfering with their alliance.
The Borgia dispatched a force of mercenaries to disrupt the agreement, but they were quickly intercepted by members of the Italian Assassins, who set their ship aflame before they could depart. Later on, the Assassins established a guild of their own in Constantinople, so as to keep their enemies in check.
By 1511, the Templars had started to relocate themselves to Constantinople, threatening to destabilize the entire region. After traveling to Masyaf to rediscover his Assassin heritage, Ezio Auditore, Grand Master of the Assassin Order and direct descendant of Altaïr, left for Constantinople to once more continue the fight against his arch-enemies, and return the seals of Altaïr to Masyaf.