Constantinople had been an imperial capital since its consecration in 330 under Roman Emperor, Constantine the Great. In the following eleven centuries, the city had been besieged many times but was captured only once: during the Fourth Crusade in 1204.:304 The crusaders established an unstable Latin state in and around Constantinople while the remaining empire splintered into a number of Byzantine successor states, notably Nicaea, Epirus and Trebizond. They fought as allies against the Latin establishments, but also fought among themselves for the Byzantine throne. The Nicaeans eventually reconquered Constantinople from the Latins in 1261. Thereafter, there was little peace for the much-weakened empire as it fended off successive attacks by the Latins, the Serbians, the Bulgarians, and, most importantly, the Ottoman Turks. The Black Plague between 1346 and 1349 killed almost half of the inhabitants of Constantinople. The city was severely depopulated due to the general economic and territorial decline of the empire, and by 1453 consisted of a series of walled villages separated by vast fields encircled by the fifth-century Theodosian walls. By 1450 the empire was exhausted and had shrunk to a few square miles outside the city of Constantinople itself, the Princes' Islands in the Sea of Marmara, and the Peloponnese with its cultural center at Mystras. The Empire of Trebizond, an independent successor state that formed in the aftermath of the Fourth Crusade, also survived on the coast of the Black Sea.

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