Constantinople began to decline after the Fourth Crusade, during which it was sacked and pillaged. The city subsequently became the center of the Latin Empire, created by Catholic crusaders to replace the Orthodox Byzantine Empire, which was divided into splinter states.However, the Latin Empire was short-lived, and the Byzantine Empire was restored, weakened, in 1261. Constantinople's churches, defenses, and basic services were in disrepair,and its population had dwindled to forty thousand from nearly half a million during the 9th century
Various economic and military policies instituted by Andronikos II, such as the reduction of forces, weakened the empire and left it more vulnerable to attack. In the mid-14th century, the Ottoman Turks began a strategy by which they took smaller towns and cities over time, cutting off Constantinople's supply routes and strangling it slowly.Finally, on 29 May 1453, after an eight-week siege (during which the last Roman Emperor, Constantine XI, was killed), Sultan Mehmed II "the Conqueror" captured Constantinople and declared it the new capital of the Ottoman Empire. Hours later, the sultan rode to the Hagia Sofia and summoned an imam to proclaim the Islamic creed, converting the grand cathedral into an imperial mosque.