Siege of Constantinople (1235–1236)

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For other sieges of the city, see list of sieges of Constantinople.

Siege of Constantinople (1235–1236)
Part of the Nicaean–Latin wars Bulgarian–Latin wars
Map showing Constantinople and its walls during the Byzantine era
Date 1235–1236 Location Constantinople, Latin Empire (modern-day Istanbul, Turkey) Result Latin victory
Belligerents
Empire of Nicaea Bulgarian Empire	Latin Empire Republic of Venice Kingdom of Morea[a] Republic of Genoa[a] Republic of Pisa[a]
Commanders and leaders
John III Vatatzes Ivan Asen II Manuel Doukas Michael II Komnenos Doukas	John of Brienne Angelo Sanudo Geoffrey II of Villehardouin John of Béthune
Strength
Unknown	Unknown
Casualties and losses
Unknown	Unknown

The siege of Constantinople (1235–1236) was a siege on the capital of the Latin Empire under Latin Emperor John of Brienne by a joint Bulgarian–Nicaean army led by the Tsar Ivan Asen II of Bulgaria and the Emperor of Nicaea John III Doukas Vatatzes.

Despite their combined strength against a small garrison, the siege failed to breach Constantinople's fortifications supported by the Venetian navy. The allied army withdrew in the autumn for the winter and renewed the siege in 1236. Later that year Asen shifted his allegiance, presumably to avoid calls for a crusade from the pope or because sought to capture the city himself, before ultimately abandoning the Latin Empire a year later and refraining from future campaigns. While the siege did not topple the Latin Empire, it increased pressure against Latin‐rule and foreshadowed the eventual Byzantine recovery of Constantinople in 1261 by the Nicaean forces.

Background

Further information: Struggle for Constantinople (1204–1261)

Coin depicting Tsar Asen (left) and portrait of Nicaen Emperor Vatatzes (right)

The Fourth Crusade resulted in the partition of Byzantine empire's territories among the crusaders. Starting in 1204, the newly established Latin Empire struggled to consolidate their power,^[1] as its authority was immediately challenged by Byzantine rump states (Nicaea and Epirus). Meanwhile, in the north, Bulgarian gathered an army aimed to control parts of Macedonia and Thrace, regions claimed by the newly established Latin Empire.^[2]

The struggle for control of Macedonia and Thrace between the different regional powers, often forming and breaking agreements between them, led much destruction to cities of north Greece, such as Serres and Philippopolis, which weakened the economic support of Constantinople. After the death of Robert of Courtenay in 1228, John of Brienne became the new Emperor of the Latin Empire. The Epirote defeat by the Bulgarians at the Battle of Klokotnitsa (1230), renewed the communication between Nicaea and the Bulgarians for an alliance against the Latin Empire.^[3]

Alliance

In the spring of 1235, Varatzes crossed the Dardanelles and took over Gallipoli. Asen along with his family arrived there to meet with Vatatzes and his court, where they concluded an alliance for a joint campaign against the Latin Empire. Part of the agreement for the alliance was the recognition of the Bulgarian Church's autocephaly by the Nicaean church, granting the title of Patriarch of Bulgaria to the archbishop of Tărnovo. In return, Nicaean patriarch was recognized by Asen as ecumenical and he gave up his claims over Mount Athos, along with ecclesiastical authority in the areas of eastern Thrace and Thessaloniki.^[4] The alliance was sealed with the marriage between Asen's daughter, Elena, and the Nicean heir, Theodore. The joint campaign started the summer of the same year right after the marriage.^[5][6]

Siege

The Nicaean army moved from Gallipoli north, seizing territories from Latin Empire in Thrace from the east coast up to the mouth of the Marica, including the fortress of Tzurulum located west of Constantinople. Having secured the surrounding territory, the two armies joined forces to lay siege to Constantinople.^[7]

The Latin Emperor had at his command a small garrison, which included 160 knights. The defenders were able to repel the besieging forces. The Nicaean fleet tried to penetrate the defenses of the Golden Horn but it was partially destroyed by the Venetians, who had send a naval squadron for the defense of Constantinople. The joint Bulgarian–Nicaean siege was unsuccessful and they retreated in the autumn due to the incoming winter. Asen and Vatatzes agreed to continue the siege in the following year and after the departure of the Venetian fleet.^[8]

The second phase of the siege, lasting into the spring of 1236, brought no significant progress. The defenders had received assistance from Geoffrey II Villehardouin of Morea and the Italian republics (Venice, Genoa and Pisa).^[7][8]

Aftermath

Bulgarian reversals

Political map of southeastern Europe c. 1210

The alliance between Asen and Vatatzes was short-lived and instead allied with the Latin Empire. Asen's army reinforced by displaced Cumans from the Steppe by the Mongols attacked the Nicaean possessions, including the fortress of Tzurulum.^[9] Scholars have presented two plausible explanations for this action. He may had reconsidered the agreement upon realizing that Nicaea stood to gain the most. If Constantinople was captured, it would had become the center of a Greek Empire preventing in the future its capture by Bulgarians.^[7] At the same time, Pope Gregory IX increased calls for a crusade against him, particularly urging Hungary to attack from the north, because Asen refused to accept union with the Church of Rome and instead he allied with schismatic opponents against Catholic-held territories. Asen managed to avert this threat through diplomatic outreach to Hungary and Constantinople and by refraining from further attacks.^[10][11]

Asen broke his alliance with the Latin Empire by the end of 1237 and made a treaty with Vatatzes. According to contemporary historian, George Akropolites, this reversal was prompted by the sudden death of his wife and one of his children from a plague outbreak, which was interpreted as divine punishment for breaking his previous alliance.^[4]

In the years that followed, Asen focused on consolidating Bulgaria's defenses and improving relations with Hungary. The kingdom faced threats not only from a potential crusade but also from the northeast, where the Mongols and Tatars had destroyed the Cuman state. This new danger imperiled both Bulgaria and Hungary and effectively halted any potential expansions to the south.^[12]

Latin Empire

After the dissolution of the besieging army, some of John of Brienne's soldiers left his service because they were not paid, further weakening the defenses of the city.^[13] In 1237, the emperor recruited Western knights for the defense of the city in his trip west with the help of the pope.^[10] Two years later, more knights (estimated 30,000 to 60,000 in number) were mobilized. They crossed Hungary and Bulgaria, where Asen not wanting to fight them gave them free passage. They captured the Nicaean fortress of Tzurulum before dispersing, many returning home and others joining in the defense of Constantinople.^[14] The sporadic reinforcements were insufficient to counter the pressure from Nicaean and Bulgarian campaigns, the capital of the Latin Empire was spared only because of the divisions among its enemies.^[7]

Nicaean actions

Vatatzes expanded his holdings in Thrace during the campaign and a year after Asen's death in 1241, he was able to secure Thessaloniki, isolating Constantinople.^[15] At the same time, Vatatzes had to return to defend his homeland in Anatolia against a possible Mongol invasion. Nicaea was spared, because the Mongols retreated following the sudden death of Great Khan in Karakorum. It was a boon for Nicaea because Mongols had inflicted great damage to the Seljuk Empire, leaving Nicaea in a stronger position to claim Constantinople.^[16]

In 1258, the Battle of Pelagonia signaled the beginning of the end of Latin predominance in Greece. On 25 July 1261, with most of the Latin troops away on campaign, the Nicaean general Alexios Strategopoulos found an unguarded entrance to the city, and entered it with his troops, restoring the Byzantine Empire under Michael VIII Palaiologos.^[17]

See also

• Byzantine Empire portal