of Pliska, and its diocese covered the whole territory of the Bulgarian state. The tug-of-war between Rome and Constantinople was resolved by putting the Bulgarian archbishopric under the jurisdiction of the Patriarch of Constantinople and the Orthodox Church, from whom it obtained its first primate, its clergy, and theological books. Although the archbishopric enjoyed full internal autonomy, the goals of Boris I were scarcely fulfilled. A Greek liturgy offered by a Byzantine clergy furthered neither the cultural development of the Bulgarians, nor the consolidation of the Bulgarian Empire; it would have eventually resulted in the loss of both the identity of the people and the statehood of Bulgaria. Following the Byzantine theory of "Imperium sine Patriarcha non staret", which said that a close relation should exist between an Empire and Patriarchate, Boris I greeted the arrival of the disciples of the recently deceased Saints Cyril and Methodius in 886 as an opportunity. Boris I gave them the task of instructing the future Bulgarian clergy in the Glagolitic alphabet and the Slavonic liturgy prepared by Cyril. The liturgy was based on the vernacular of the Bulgarian Slavs from the region of Thessaloniki. In 893, Boris I expelled the Greek clergy from the country and ordered the Greek language to be replaced with the Slav-Bulgarian vernacular. Autocephaly and Patriarchate Following Bulgaria's two decisive victories over the Byzantines at Acheloos (near the present-day city of Pomorie) and Katasyrtai (near Constantinople), the government declared the autonomous Bulgarian Archbishopric as autocephalous and elevated it to the rank of Patriarchate at an ecclesiastical and national council held in 919. After Bulgaria and the Byzantine Empire signed a peace treaty in 927 that concluded the 20-year-long war between them, the Patriarchate of Constantinople recognised the autocephalous status of the Bulgarian Orthodox Church and acknowledged its patriarchal dignity. The Bulgarian Patriarchate was the first autocephalous Slavic Orthodox Church, preceding the autocephaly of the Serbian Orthodox Church (1219) by 300 years and of the Russian Orthodox Church (1596) by some 600 years. It was the sixth Patriarchate after the Pentarchy patriarchates of Rome, Constantinople, Alexandria, Antioch and Jerusalem. The seat of the Patriarchate was the new Bulgarian capital of Preslav. The Patriarch was likely to have resided in the town of Drastar (Silistra), an old Christian centre noted for its martyrs and Christian traditions. Ohrid Archbishopric On April 5, 972, Byzantine Emperor John I Tzimisces conquered and burned down