Battle of Philippopolis ( 1208 ) The Battle of Philippopolis or battle of Plovdiv ( ) took place on 30 June 1208 in the surroundings of Plovdiv , Bulgaria between the armies of the Bulgarian Empire and the Latin Empire . The Crusaders were victorious . Origins of the conflict . After the armies of the Fourth Crusade seized the Byzantine capital Constantinople in 1204 they established a new empire on previously Byzantine territories and continued to fight the states which emerged from the Byzantine Empire - the Despotate of Epiros in Europe and the Nicaean Empire in Asia Minor . Its Emperor Baldwin I rejected the peace proposal of the Bulgarian Emperor Kaloyan and on the following year the Crusader army was annihilated by the Bulgarians in the battle of Adrianople and Baldwin himself was captured and died as a prisoner in Tarnovo . However , Kaloyan was murdered during the siege of Thessalonike in 1207 . The conspirators were organized by his cousin Boril who succeeded the Bulgarian crown . The new Emperor had to cope with the supporters of the country ' s legitimate heir Ivan Asen II who was juvenile at that time . This gave precious time for the Latin Empire to reorganize . The battle . In the spring of 1208 Boril considered that the internal situation in Bulgaria had calmed down and turned his attention to the foreign - political affairs . It seems that he supported the policy of his predecessor and continued the war against the Latin Empire . The Bulgarian army invaded Thrace and defeated the Crusaders near Stara Zagora . Inspired , Boril marched southward and on 30 June 1208 he encountered the main Latin army . The Bulgarian army outnumbered its enemy - Boril had 33 , 000 soldiers while Henry had 2 , 000 knight s and several thousand soldiers . Boril tried to apply the same tactics which Kaloyan used at Adrianople - the light cavalry tried to harass the Crusaders , to stretch their line and to lead them towards the main Bulgarian forces . The knights , however , had learned the bitter lesson from Adrianople and did not repeat the same mistake . Instead , they organized a trap and attacked the detachment which was personally commanded by the Tsar . Boril had 1 , 600 men and could not withstand the enemy assault and fled after which the whole Bulgarian army pulled back . The Bulgarians knew that the enemy would not chase them in the mountains so they retreated towards one of the eastern passes of the Balkan mountains , Turia . The Crusaders who followed the Bulgarian army were attacked in a hilly country near the contemporary village of Zelenikovo by the Bulgarian rear guard and after a bitter fight they were defeated . However , they did not collapse as the main Latin forces arrived . The battle continued for a very long time and finally the Bulgarians retreated to the north when the bulk of their army had safely passed through the mountains . The Crusaders also retreated to Plovdiv . Aftermath . The defeat was not disastrous and on the following year the war waged with unceasing rage . Boril was energetic and persistent but he could never fulfill his plans . In 1209 Henry managed to win over Alexius Slav who ruled the Rhodopes and married his daughter to the Bulgarian noble . To compensate that , Boril had to arrange an alliance with his brother Strez who ruled in Prosek - Strez received the high title " sevastokrator " and the right to govern his lands freely . In 1211 the Bulgarians formed an alliance with the Niceans but the allies could not take Constantinople . After that failure Boril reorientated his policy and the two Empires settled peace after the marriage of Kaloyan ' s daughter Maria of Bulgaria and the Latin Emperor Henry .