At first this new power controlled only the environs of Constantinople and the province of Thrace, but eventually it expanded into Bithynia, Thessaly and central and southern Greece.

This might have made for good relations between Tsar Kaloyan and the new Western European conquerors, but immediately after settling in Constantinopole the Latins stated their pretensions on Bulgarian lands.

These belligerent actions convinced the Bulgarian Emperor to abandon the prospect of a Latin alliance, turning instead to the Greeks in the unconquered regions of Thrace.

In front of each gate of the castle walls a unit was placed, which notably included a Venetian contingent led by Doge Enrico Dandolo.

Honouring his obligations to the rebellious Greeks, Tsar Kaloyan arrived with his army and encamped approximately 25 kilometers northeast of the city on April 10, 1205.

Numerous researchers pinpoint the location of the battle north of Adrianople and near the keep of Vukelon - K. Jireče, V. Guzelev, St. Boyadjiev - yet there is no conclusive evidence.

The total number of troops was no greater than four thousand, yet it is not clear how many soldiers took part in the battle and how many stayed under the walls to continue the siege.

Although they do not take part in the battle itself, all of the Byzantine rebels from East Thrace had gathered at Adrianopole and stood bravely to defend its wall from the conquerors.

Baldwin made the decision to wait for all of the remaining knights and soldiers to gather and prepare for a proper battle, which would take place after the upcoming Easter celebrations.

During the preparation for the ambush, the Bulgarians dug trous de loup or "wolf pits", in order to create obstacles for the movement and battle formation of the heavy cavalry knights.

Kaloyan placed the infantry first in the ambush with the heavy cavalry in reserve, ready to intervene if the foot soldiers began to give in to the Latins.

On Thursday, 14 April 1205, during the celebration of Catholic Easter, the Cuman light cavalry made a sweeping attack on the camp of the knights with arrows, loud yells and ringing of steel.

Count Louis I of Blois disregarded the plan made the night before and led his unit after the Cumans, and the other soldiers, already blinded by anger, followed his lead.

After his capture by the Bulgarians, the fate of Emperor Baldwin I was unknown to his subjects; his brother Henry of Flanders assumed regency in his absence.

The historian George Acropolites reports that the Tsar had Baldwin's skull made into a drinking cup, as had happened to Nikephoros I almost four hundred years before, but no evidence has been found to confirm this.