There were many 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.
Turkic, Persian, Avar, Slavonic and Arab sieges
Siege of Constantinople (559), by the Kutrigurs, unsuccessful
Siege of Constantinople (626), by Avars, Slavs, and the Sassanid Persians, unsuccessful
Siege of Constantinople (654), by the Umayyad Caliphate following the Battle of the Masts, unsuccessful
Siege of Constantinople (674–678), by the Umayyad Caliphate, unsuccessful
Siege of Constantinople (717–718), by the Umayyad Caliphate, unsuccessful
Siege of Constantinople (813), by Krum of Bulgaria, unsuccessful
Siege of Constantinople (860), by the Rus', unsuccessful
Siege of Constantinople (907), by the Rus' in 904/907, unsuccessful
Siege of Constantinople (941), by the Rus', unsuccessful
Sieges and attacks during Byzantine civil wars
Siege of Constantinople (821–822), by rebel forces under Thomas the Slav
Siege of Constantinople (1047), by rebel forces under Leo Tornikios
Siege of Constantinople (1376), a 32-day siege by Andronikos IV Palaiologos with the support of the Ottoman Turks
Siege of Constantinople (1203), first siege by the Fourth Crusade, in which Alexius IV was able to usurp the throne after Alexius III fled to Thrace; objectives achieved and the siege lifted
Sack of Constantinople (1204), second siege by the Fourth Crusade, in which the Byzantines were overwhelmed and the city thoroughly sacked, successful
Siege of Constantinople (1235), by Bulgarian and Nicaean forces, unsuccessful
A Nicaean attack on Constantinople is implied by George Akropolites's account for 1248, but no details are known
Siege of Constantinople (1260), by the Empire of Nicaea, unsuccessful
In 1261, a small force of Nicaean troops under Alexios Strategopoulos gained entry into the poorly defended Latin capital, ending the Latin Empire and restoring Byzantine rule to the City. Most Latin troops defending the city were absent on campaign, and the Emperor fled without putting up any resistance; there was no siege.
An Ottoman blockade between 1390 and 1402, first interrupted by the Crusade of Nicopolis, then lifted due to the Battle of Ankara
Siege of Constantinople (1411), a short Ottoman siege that occurred during the Ottoman Interregnum, unsuccessful
Siege of Constantinople (1422), the first large-scale siege of the city by the Ottomans, unsuccessful
Fall of Constantinople in 1453, after an Ottoman siege, successful
List of sieges of Constantinople Wikipedia (Text) CC BY-SA
