The Muslim Ottoman Turks on May 29, 1453,conquered the capital of the Greek Christian Byzantines and held the Christian Greeks under for 4 centuries till they got back their independence on 1821.
The Fall of Constantinople (Greek: Ἅλωσις τῆς Κωνσταντινουπόλεως, Halōsis tēs Kōnstantinoupoleōs; Turkish: İstanbul’un Fethi Conquest of Istanbul) was the capture of the capital of the Byzantine Empire by an invading Ottoman army on 29 May 1453. The attackers were commanded by the then 21-year-old Sultan Mehmed II, who defeated an army commanded by Emperor Constantine XI Palaiologos and took control of the imperial capital, ending a 53-day siege that had begun on 6 April 1453. After conquering the city, Sultan Mehmed transferred the capital of his Empire from Edirne to Constantinople, and established his court there.
The capture of the city (and two other Byzantine splinter territories soon thereafter) marked the end of the Byzantine Empire, a continuation of the Roman Empire, an imperial state dating to 27 BC, which had lasted for nearly 1,500 years. The conquest of Constantinople also dealt a massive blow to Christendom, as the Muslim Ottoman armies thereafter were left unchecked to advance into Europe without an adversary to their rear.
It was also a watershed moment in military history. Since ancient times, cities had used ramparts and city walls to protect themselves from invaders, and Constantinople’s substantial fortifications had been a model followed by cities throughout the Mediterranean region and Europe. The Ottomans ultimately prevailed due to the use of gunpowder (which powered formidable cannons).
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 Medieval period.