As the defence forces of the city had fled, Isbul and Malamir entered negotiations with the population in order to persuade them to cede the fortress. Pavlov is of the opinion that the war ended with a continuation of the peace of 815. He believes that Byzantine Emperor Theophilos (r. 829–842) was forced to make concessions to Bulgaria, which may have included the incorporation of Philippopolis and its close surroundings into the Bulgarian Empire. During his time as co-ruler and kavhan of Malamir, Isbul financed the construction of a water conduit (aqueduct) or fountain in Pliska, which he donated to Malamir. That construction was the occasion for a great feast, which the ruler organised, and for gifts to the nobility, all of it testifying to Isbul's affluence. In the source about the construction, Isbul is hailed alongside Malamir: "May God let the God-appointed ruler live a hundred years together with the kavhan Isbul". Normally, such blessings were only directed at the ruler, and this is the only case from the First Bulgarian Empire which references another person. The inscription also mentions Isbul's old age at the time. After the surprise death of Malamir in 836, the Bulgarian throne passed to Presian I (836–852), who too was likely underage. As evidenced by the Presian Inscription from Philippi, Isbul retained his position as kavhan and his decisive influence in the Bulgarian court. In 837, the Slavic tribe of the Smolyani (Smolenoi), who inhabited the lower Nestos (Mesta) River and Western Thrace near Drama, rose against their Byzantine rulers. The inscription of Philippi mentions large-scale Bulgarian activity in the lands of the Smolyani. The Bulgarian forces were led by Isbul, as well as the ichirgu-boil (commander of the capital garrison) and the head priest. As the inscription is damaged, it is unclear who Presian and Isbul supported in that conflict. However, during this campaign the Bulgarian army conquered most of Macedonia including Philippi, where the inscription was found. From that point on, Isbul disappears from the sources, and there is no information about the date and circumstances of his death. Assessment and legacy In his biography of Isbul, Pavlov underlines his "extraordinary merits for the development of the Bulgarian state" and describes him as "one of the architects of medieval Bulgarian statehood during the years of its rise". Romanian historian Florin Curta emphasises the similarity of Isbul's role to that of 8th-century Mayors