Siege of Constantinople
1235 CE.
Shown on the map at 41.008°, 28.975°.
The siege of Constantinople took place between 1235 and late 1236 when a joint Bulgarian–Nicaean army led by Tsar Ivan Asen II of Bulgaria and Emperor of Nicaea John III Doukas Vatatzes conducted an unsuccessful siege of the capital of the Latin Empire. The siege arose from the prolonged conflict between the Latin Empire, Bulgaria and the Byzantine successor states, the Empire of Nicaea and Despotate of Epirus, following the capture and sack of Constantinople by the Fourth Crusade in 1204. Each aimed to revive or establish an empire in the territories of the Byzantine Empire. Initially, Asen was led by the Latins to believe he would become emperor of Constantinople following the death of Robert of Courtenay in 1228. The Latins terminated negotiations after the Bulgarians defeated Epirus at the Battle of Klokotnitsa in 1230, as the Latins sought only to prevent an alliance between Bulgaria and Epirus. The announcement that John of Brienne had become the new Latin emperor angered Asen. He initiated negotiations and eventually agreed to a formal alliance with Vatatzes in early 1235 to combine their forces to reclaim Constantinople.
Text from the Wikipedia article Siege of Constantinople (1235–1236), licensed CC BY-SA 4.0.