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Brief war with Theophilos

After the expiration of the original 20-year peace treaty with the Byzantine Empire in 836, Emperor Theophilos ravaged the regions within the Bulgarian frontier. The Bulgars retaliated, and under the leadership of Isbul, the minister of Malamir, they reached Adrianople. At this time, if not earlier, the Bulgars captured Philippopolis (Plovdiv) and its environs. Several surviving monumental inscriptions from this reign make reference to the Bulgar victories and others to the continuation of construction activities in and near Pliska. The war ended, however, when Slavs in the vicinity of Thessalonica rebelled against the Byzantine Empire in 837.

Emperor Theophilos sought Bulgar support in putting down the rebellion, but he simultaneously arranged for his fleet to sail through the Danube delta and undertake a clandestine evacuation of some of the Byzantine captives settled in trans-Danubian Bulgaria by Krum and Omurtag. In retaliation Isbul campaigned along the Aegean coasts of Thrace and Macedonia and captured the city of Philippi, where Theophilos set up a surviving memorial inscription in a local church. Isbul's campaign may have resulted in the establishment of Bulgar suzerainty over the Slavic tribe of the Smoljani.