The renowned Bulgarian medievalist Vasil Zlatarski assumes that in the aftermath of the major Bulgarian victory over the Byzantine Empire in the battle of Achelous in 917, the Bulgarian monarch Simeon I (r. 893–927) summoned a church council in 918 in order to raise the autocephalous Bulgarian Archbishopric to a completely independent Patriarchate. After the triumph at Achelous, Simeon I demanded that Byzantines recognize him not only as Emperor of the Bulgarians, which they already did in 913, but also of the Romans. Zlatarski argues that the first act of Simeon I after the battle was to raise the statute of the Bulgarian Orthodox Church, because according to the Byzantine imperial tradition the autocrat must have a patriarch and there could be no empire without a Patriarchate.