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.

History
Around 1209, the city was visited by the 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 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

 * Constantinople Concept.jpg 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 of not corresponded with the overall storyline.
 * In the E3 Demo Interview for Assassins Creed Revelations is is said that Constaninople will be slightly smaller than Rome, but will have more buildings, and be more densly populated.