Mehmed II granted his soldiers three days to plunder the city, as he had promised them and in accordance with the custom of the time.^[20] Soldiers fought over the possession of some of the spoils of war. On the third day of the conquest, Mehmed II ordered all looting to stop and issued a proclamation that all Christians who had avoided capture or who had been ransomed could return to their homes without further molestation, although many had no homes to return to, and many more had been taken captive and not ransomed.

Mehmed himself knocked over and trampled on the altar of the Hagia Sophia. He then ordered a muezzin ascend the pulpit and sound a prayer. The Hagia Sophia was converted into a mosque, but the Greek Orthodox Church was allowed to remain intact and Gennadius Scholarius was appointed Patriarch of Constantinople.

With the capture of Constantinople, Mehmed II had acquired the future capital of his kingdom, albeit one in decline due to years of war. The fall of Constantinople shocked many Europeans, who viewed it as a catastrophic event for their civilization. Many feared other European Christian kingdoms would suffer the same fate as Constantinople. The loss of the city was a crippling blow to Christendom, and it exposed the Christian West to a vigorous and aggressive foe in the East. The Christian reconquest of Constantinople remained a goal in Western Europe for many years after its fall to the Ottoman Empire. Rumours of Constantine XI's survival and subsequent rescue by an angel led many to hope that the city would one day return to Christian hands. Pope Nicholas V called for an immediate counter-attack in the form of a crusade, however no European powers wished to participate, and the Pope resorted to sending a small fleet of 10 ships to defend the city. The short lived Crusade immediately came to an end and as Western Europe entered the 16th century, the age of Crusading began to come to an end.