Mehmed II entered the city in the afternoon on the first day of the conquest. He went to Hagia Sophia-now a mosque-and prayed there, saying: "My throne is Istanbul from now on."
Constantinople was conquered after a siege that lasted for 54 days with intervals.
The conquest ended the 1,058-year-old Byzantine Empire, brought the Middle Ages to a close, and made Istanbul the proud new capital of the Ottoman Empire.
Ilhami Danis, a historian at Istanbul's Fatih Sultan Mehmed Vakif University, told Anadolu Agency that the city was a key target both logistically and strategically as the Ottoman Empire's connections from Anatolia to Rumelia (the Balkans) and the rest of Europe mostly went through Gallipoli (Gelibolu, in nearby Canakkale).
Danis said the conquest was important both for the continuation of Ottoman conquests into Europe and for controlling the traffic between the Mediterranean and the Black Sea.
Feridun Emecen, the dean of Istanbul's 29 Mayis University's Faculty of Literature, stressed the strategic location of Istanbul, adding that the city carries great religious importance for Christians and Muslims alike.
"A new empire was born with the conquest of Istanbul by Mehmed II, and Mehmed II, in a way, became the founder of the Ottoman Empire by conquering Istanbul. Therefore, the conquest, which is a turning point, holds great importance for Turkish history," Emecen said.
Emecen noted that the conquest of Istanbul led to a perception of threat mixed with fear in the Western world.
After the conquest, calls for the establishment of a new Crusader army began to be made in the Western world, he added.
The conquest was met with elation in the Muslim world, except for the Mamluk administration, Emecen said, adding that it was also mostly welcomed in Turkish Anatolia, except for the Karamanids.