After ten centuries of wars, defeats, and victories, the Byzantine Empire came to an end when Constantinople fell to the Ottoman Turks in May 1453. The city’s fall sent shock waves throughout Christendom. It is widely quoted as the event that marked the end of the European Middle Ages.

By the mid-fifteenth century the Byzantine Empire had long been in decline, but it remained an important bastion of Christian Europe facing Muslim Asia. The Ottoman Turks, however, had extended their territories to include the Balkans as well as Anatolia. Only Constantinople held out behind its supposedly impenetrable walls. For the Ottomans, the city had enormous prestige, both as a center of the rival Christian faith and a symbol of imperial power. An attempted siege conducted by Sultan Murad the Second in 1422 failed, but Murad’s young successor, Mehmed the Second, was determined to carry out the operation that would cap all previous Turkish triumphs.

When Mehmed the Second set out to take Constantinople in the spring of 1453, the city was a shadow of its former glory, but it remained highly difficult to capture by assault. Its formidable fortifications had held out through numerous sieges in the past. Mehmed besieged the city in early April with a force of between 75,000 and 100,000 and a large fleet. His preparations were extensive. He employed a Hungarian artillery expert, Urban, to build him the most powerful cannon ever seen to batter the city’s walls.

On 29 May, Mehmed launched simultaneous assaults from the sea and land sides of the city and overcame the defenders. Pouring into the city through one of the gates that was forced (some claimed that it had been unlocked), the Ottomans killed the emperor as he attempted a counterattack with his remaining defenders. Mehmed, still only twenty years old, rode a white horse through the streets to Hagia Sophia, Constantinople’s famed cathedral, which was immediately used as a mosque to say prayers of thanks for victory.

The fall of Constantinople was a huge blow for the Christian world but, although Pope Nicholas the Fifth called for a crusade to regain the city for Christendom, no concerted military response was made. Now styled "the Conqueror," Mehmed declared the city his new capital and claimed to be the rightful successor to the fallen Roman Empire.