The Latin Empire suffered heavy casualties and in the fall of 1205 the Crusaders tried to regroup and reorganize the remains of their army. Their main forces consisted of 140 knights and several thousand soldiers based in Rusion. This army was led by Thierry de Termonde and Thierry de Looz who were among the most notable nobles of the Latin Empire of Constantinople.

The battle of Rusion occurred in the winter of 1206 near the fortress of Rusion (Rusköy contemporary Keşan) between the armies of the Bulgarian Empire and the Latin Empire of Byzantium. The Bulgarians scored a major victory.

In the whole military operation the Crusaders lost more than 200 knights, many thousands of soldiers and several Venetian garrisons were completely annihilated. The new Emperor of the Latin Empire Henry of Flanders had to ask the French King for another 600 knights and 10,000 soldiers. Geoffrey of Villehardouin compared the defeat with the disaster at Adrianople. However, the Crusaders were lucky - in 1207 Tsar Kaloyan was killed during the siege of Thessaloniki and the new Emperor Boril who was a usurper needed time to enforce his authority.