[1][2][3] According to De Administrando Imperio, the Serbs and Bulgars had lived peacefully as neighbours until the Bulgarian invasion in 839 (in the last years of emperor Theophilos).

Khan Presian (r. 836–852) launched an invasion into Serbian territory in 839, which led to a war that lasted for three years, in which the Serbs were victorious.

[10] The defeat of the Bulgars, who had become one of the greater powers in the 9th century showed that Serbia was an organized state, fully capable of defending its borders; a very high military and administrative organizational frame to present such effective resistance.

[11] Soon after 846, with the end of the 30–year–peace established by the Byzantine–Bulgarian Treaty of 815, Presian and his first minister Isbul invaded the regions of the Struma and the Nestos, and empress–regent Theodora (r. 842–855, the wife of Theophilos) answered by attacking Thracian Bulgaria.

[5] A brief peace was concluded, then Presian proceeded to invade Macedonia[5][4][7] and eventually most of the region, including the city of Philippi, were incorporated in Bulgaria.