The Fall of Constantinople occurred after a siege during which the Ottoman Empire under the command of Sultan Mehmed II attempted to capture the capital of the Byzantine Empire, Constantinople which was defended by the army of Emperor Constantine XI. The siege lasted from Thursday, 5 April 1453 until Tuesday, 29 May 1453 (according to the Julian Calendar), when the city fell to the Ottomans. The event marked the end of the political independence of the millennium-old Byzantine Empire, which was by then already fragmented into several Greek monarchies.
Following his accession to the Ottoman throne, Mehmed had been applying pressure on Constantinople and the Byzantines by building forts along the Dardanelles. On 5 April, he laid siege to Constantinople with an army numbering 80,000 to 200,000 men. The city was defended by an army of 7,000 of whom 2,000 were foreigners. The siege began with heavy Ottoman artillery firing at the city's walls while a smaller Ottoman force captured the rest of the Byzantine strongholds in the area. Ottoman attempts to blockade the city completely failed at first owing to the boom blocking the entrance to the Golden Horn thus allowing four Christian ships to enter the city. Mehmed had his ships rolled into the Golden Horn on greased logs and a Byzantine effort to destroy the ships with fire ships failed, allowing the Ottomans to seal the city off.
The Turkish frontal assaults on the walls were all repulsed with heavy casualties and the Turkish attempts to undermine the walls were all countered and abandoned. Mehmed's offer to lift the siege, if he was given the city, was rejected. On 22 May, the moon rose in eclipse prophesying the fall of the city and a few days later Constantine received news that no Venetian relief fleet was coming. After midnight of the 29, the Ottoman army attacked the walls. The first wave of irregulars was thrown back. The second Turkish wave of Anatolians managed to breach the Blachernae section of walls. The defenders pushed back the Anatolians and managed to hold out against the Sultan's elite Janissaries. During the fighting, the Genoese commander, Giovanni Giustiniani was fatally wounded and retreated to his ships with his men. The Emperor and his men continued to hold off the Turks until the Turks discovered an unlocked gate upon which they flooded into the city. Constantine reportedly fell leading a charge against the invaders, though his body was never found. The last defenders were subdued and the Turks proceeded to loot the city.
This battle marked the end of the Byzantine Empire, an empire which had lasted for over 1,100 years. The city's fall was a massive blow for Christendom. Pope Nicholas V ordered an immediate counter-attack, but his death soon after marked the end of the plan. Mehmed made Constantinople his capital and proceeded to conquer the last two Byzantine states, the Despotate of Morea and the Empire of Trebizond. Many Greeks fled the city and migrated to other parts of Europe, in particular Italy. This move is thought to have helped fuel the Renaissance. The Fall of Constantinople is seen by some scholars as being a key event in leading to the end of the Middle Ages, and some mark the end of the Middle Ages by this event.