his brother's co-ruler in 1187 or 1188. The Byzantines launched a series of unsuccessful campaigns against the rebellious Bulgarians and Vlachs, but they could not prevent Peter and Asen from securing their rule in Paristrion. Isaac II personally led his troops against the brothers' realm and laid siege to Lovech in the spring of 1188. Although he could not occupy the fortress, the Byzantines captured Asen's wife, Helen, and his younger brother, Kaloyan. He was held hostage in Constantinople for years. The arrival of the crusader army of the Holy Roman Emperor, Frederick Barbarossa, in the Balkan Peninsula in July 1189 enabled Peter and Asen to occupy new territories of the Byzantine Empire. One of the chronicles of Barbarossa's crusade, The History of the Expedition of the Emperor Frederick, explicitly mentions that they seized "the region where the Danube flows into the sea" (present-day Dobruja) and parts of Thrace. When writing of the negotiations between Barbarossa and the brothers' envoys during the march of the crusaders across the Balkans, primary sources mention only Peter, suggesting he was regarded as the senior ruler of Bulgaria. The crusaders left the Balkans for Asia Minor in March 1190. Shortly after the crusaders' departure, Isaac II Angelos moved into the lands under the rule of Peter and Asen. He could not defeat the Vlachs and Bulgarians, because they avoided a pitched battle, forcing the Emperor to start to retreat. The imperial army was ambushed and defeated at a mountain pass. The victorious Vlachs and Bulgarians, along with their Cuman allies, launched new raids against Thrace, pillaging Anchialus and other towns. Isaac II defeated the Cumans near Adrianople in April 1191. Thereafter his cousin, Constantine Angelos Doukas, routed Peter and Asen's troops in a series of battles. A eulogy delivered in praise of Isaac II in 1193 referred to Asen as a "reckless and obdurate rebel", surrounded by "imperial traps", while describing Peter as a "stumbling block" and an "adverse wind" to his brother. The speech shows, Byzantine intrigues stirred up a conflict between the brothers in 1192. Madgearu says, Peter was allegedly willing to make peace with the Byzantines, but Asen wanted to continue the war. Akropolites knew that Peter moved from Tarnovo to Preslav at an unspecified date, a region known as "Peter's land" even in the 13th century. Historians Madgearu and Paul Stephenson agree, the sources provide evidence the brothers divided their