Following two decisive victories over the Byzantines at Achelous (near the present-day city of Burgas) and Katasyrtai (near Constantinople), the autonomous Bulgarian Archbishopric was proclaimed autocephalous and elevated to the rank of patriarchate at an ecclesiastical and national council held in 918 or 919. As a result of the Treaty of 927, which affirmed the Bulgarian victory in the Byzantine–Bulgarian war of 913–927, the Patriarchate of Constantinople recognized the autocephalous status of the Bulgarian Orthodox Church and acknowledged its patriarchal dignity. Thus, the Bulgarian Patriarchate became the first national patriarchate in Europe, and the sixth autocephalous patriarchate after the five forming the Pentarchy - those of Jerusalem, Antioch, Alexandria, Rome, and Constantinople. The seat of the patriarchate was the new Bulgarian capital of Preslav although the patriarch is likely to have resided in the town of Drastar (Silistra), an old Christian centre famous for its martyrs and Christian traditions.