The Ottoman Turks captured Constantinople in 1453. The conquest ended the Byzantine Empire's control of the city and established Sultan Mehmed II as one of the most important rulers of the late medieval world.
The siege began on April 6, 1453, and concluded on May 29 after 53 days. Mehmed's Ottoman army greatly outnumbered the defenders led by Byzantine Emperor Constantine XI Palaiologos. Massive cannons, including specialized bombards, helped breach the city's famous Theodosian Walls, which had protected Constantinople for centuries.
After entering the city, Mehmed made Constantinople the Ottoman capital, replacing Adrianople. He also ordered the conversion of Hagia Sophia, the Byzantine cathedral, into a mosque. The city gradually became known in Turkish usage as Istanbul, although Constantinople remained common in many contexts for centuries.
The fall is often described as marking the end of the Middle Ages and the beginning of the early modern era. It also demonstrated how gunpowder artillery was changing siege warfare. A common mistake is to confuse 1453 with 1204, when Western Crusaders captured and sacked Constantinople during the Fourth Crusade.