There were several sieges of Constantinople during the history of the Byzantine Empire. Two of them resulted in the capture of Constantinople from Byzantine rule: in 1204 by Crusaders, and in 1453 by the Ottoman Empire under Mehmed II.
Read more about Sieges Of Constantinople: Persian and Arab Sieges of Constantinople, Sieges By Bulgaria and The Rus', Sieges and Attacks During Civil Wars, Crusades, Nicaean Sieges, Ottoman Sieges, See Also