On May 29, 1453 the City of Constantinople fell to the Ottoman Turks.

The Fall of Constantinople  was the capture of the capital of the Eastern Roman (Byzantine) Empire by an invading army of the Ottoman Empire on 29 May 1453. The Ottomans were commanded by 21-year-old Ottoman Sultan Mehmed II, who defeated an army commanded by Byzantine Emperor Constantine XI Palaiologos. The conquest of Constantinople followed a 53-day siege that had begun on 6 April 1453.

The capture of Constantinople (and two other Byzantine splinter territories soon thereafter) marked the end of the Roman Empire, an imperial state that had lasted for nearly 1,500 years. The Ottoman conquest of Constantinople also dealt a massive blow to Christendom, as the Ottoman armies thereafter were left unchecked to advance into Europe without an adversary to their rear. After the conquest, Sultan Mehmed II transferred the capital of the Ottoman Empire from Edirne to Constantinople. Many Greek and other intellectuals fled the city before and after the siege, with the majority of them migrating to Italy, which helped fuel the Renaissance.

The conquest of the city of Constantinople and the end of the Byzantine Empire was a key event in the Late Middle Ages, which also marks, for some historians, the end of the Middle Ages.

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. 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 return to 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 heavily exhausted, consisting of 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.

https://en.wikipedia.org/wiki/Fall_of_Constantinople