Constantinople

"Many generations of men have ruled the city. But they have never subdued her. She always bounces back."

- Yusuf Tazim regarding Constantinople.

Constantinople, also known as Istanbul to its Turkish rulers, was the capital of the Ottoman Empire, and the only pan-continental city in the world. During the Renaissance, it was Europe's largest and wealthiest city, consisting of four distinct districts; Constantin, Beyazid, Imperial, and Galata.

Fourth Crusade
In 1204 the city was visited by the Grand Master of the Assassin Order, Altaïr Ibn-La'Ahad, who had hopes of setting up a Guild in the city. However, mass riots followed by the arrival of European Crusaders who sacked the city, forced him to retreat.

Renaissance
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 due to their defeat in Italy and the disruption of their activities throughout Europe. There they were threatening to destabilize the entire region and ultimately seize the Ottoman Empire for themselves, which was growing in wealth and power. After traveling to Masyaf to rediscover his Assassin heritage, Ezio Auditore, Grand Master of the Assassin Order left for Constantinople to retrieve the seals Altaïr had hidden across the city.

Trivia

 * Some pictures suggest that Constantinople was intended to be featured in the first Assassin's Creed game, as some concept arts show Altaïr on horseback overlooking the city. However, featuring the city would not have corresponded with the overall storyline.
 * In the E3 Demo Interview for Assassin's Creed: Revelations, it is said that Constantinople will be slightly smaller than Rome, but will have more buildings, and be more densely populated.
 * In Assassins Creed: Revelations, it has been revealed that Ezio's main enemies will be the Janissaries.
 * Alexandre Amancio, the Creative Director of the Assassin's Creed series, stated at E3 that Constantinople is a "really cool metaphor for Ezio meeting Altaïr", due to the fact that half of Constantinople was in Europe, and the other in Asia.
 * It is also stated by Darby McDevitt that Constantinople would a meaningful meeting of Ezio and Altaïr as the city itself was formerly under Christian control, then Muslim, which suits Altaïr and Ezio as the former hails from a Muslim culture in Syria and the latter hails from a Christian Italy.