[2] On 19 April 1229, Marie was betrothed to Baldwin II, junior co-ruler of her father as Emperor of the Latin Empire.

In 1235-36, Constantinople was besieged by the combined forces of Ivan Asen II of Bulgaria and John III Doukas Vatatzes of the Empire of Nicaea.

The city was defended by only its small garrison of knights, the fleet of the Republic of Venice and a minor force sent by Geoffrey II of Villehardouin, Prince of Achaea to reinforce the defense.

Baldwin II undertook another mission, heading to Western Europe in attempt of raising the funds and recruiting the armed forces needed to secure the survival of their Empire.

He returned by 8 October 1248, the date of a charter that empowered her to mortgage his western lands in order to pay the huge debt of 24,000 hyperpers.

[8] Marie arrived in Cyprus while Louis IX of France and the Crusaders were stationed there, only to have a strong winds blow her ship free of its anchor, taking it and all its cargo to Acre.

[9] For the next years Marie contested unsuccessfully with Henry V of Luxembourg for control of those properties, which were the source of income for both Emperor and Empress, until her cession of these lands and castles 17 June 1258 to Margaret II, Countess of Flanders.

[10] After this, she went to the court of Castile where she successfully raised the money to ransom her son Philip, who was held hostage by bankers in Venice and who was released at some date between June 1258 and 1 May 1261.

In July 1261, Alexios Strategopoulos, a general of Nicaea, was sent with a small advance force of 800 soldiers, most of them Cumans,[12] to keep a watch on the Bulgarians and spy out the defences of the Latins.

[13] When the Byzantine force reached the village of Selymbria, they learned from independent local farmers (thelematarioi) that the entire Latin garrison, and the Venetian fleet, were absent conducting a raid against the Nicaean island of Daphnousia.

[14] Although initially hesitant, due to both the small size of his force, which might be fatal if the Latin army returned, and because he would exceed his orders, Strategopoulos eventually decided not to lose such a golden opportunity to retake the city.

They attacked the walls from the inside, surprised the guards and opened the gate, allowing the Byzantine force entry into the city.

Fearing the revenge the Byzantines would exact upon them, the Latin inhabitants, from Emperor Baldwin II downwards, hurriedly rushed to the harbour, hoping to escape by ship.

[16] At the time the city was under the control of Michael VIII Palaiologos, the Nicaean emperor who had moved his capital to Constantinople, while the title was also claimed by William VII, Marquess of Montferrat.

He was also given suzerainty over the Principality of Achaea and sovereignty of the Aegean Islands, excepting those held by Venice and Lesbos, Chios, Samos, and Amorgos.