Fall of Constantinople Taking place on May 29, 1453, this turning point in European history marked the final conquest of the Eastern Roman or Byzantine Empire by the Ottoman Turkish Empire, a domain that covered territory in southeastern Europe, Asia Minor, the Middle East, and North Africa. Since the capture of Constantinople, the ancient capital of the Byzantine Empire, by members of the Fourth Crusade in 1204, the city and the realm had suffered a slow decline as the Ottoman Turks stepped up their attacks on Byzantine cities and ports in the Levant and Asia Minor. By the turn of the fifteenth century the Turks had built a stronghold on the southern side of the Bosporus, the strait dividing Constantinople from Asia Minor proper. The Ottoman sultan, Mehmed II, established another fortress on the European side of the Bosporus to prevent reinforcements from reaching the city from allied Black Sea ports.