The Bulgars, a Turanian race akin to the Tatars, Huns, Avars, Petchenegs and Finns, made their appearance on the banks of the Pruth in the latter part of the 7th century. They were a horde of wild horsemen, fierce and barbarous, practising polygamy, and governed despotically by their khans (chiefs) and boyars or bolyars (nobles). Their original abode was the tract between the Ural mountains and the Volga, where the kingdom of Great (or Black) Bolgary existed down to the 13th century. In 679, under their khan Asparukh (or Isperikh), they crossed the Danube, and, after subjugating the Slavonic population of Moesia, advanced to the gates of Constantinople and Salonica. The East Roman emperors were compelled to cede to them the province of Moesia and to pay them an annual tribute. The invading horde was not numerous, and during the next two centuries it became gradually merged in the Slavonic population. Like the Franks in Gaul the Bulgars gave their name and a political organization to the more civilized race which they conquered, but adopted its language, customs and local institutions. Not a trace of the Ugrian or Finnish element is to be found in the Bulgarian speech.
This complete assimilation of a conquering race may be illustrated by many parallels.
The history of the early Bulgarian dynasties is little else than a record of continuous conflicts with the Byzantine emperors. The tribute first imposed on the Greeks by Asparukh was again exacted by Kardam (791-797) and Krum (802-815), a sovereign noted alike for his cruelty and his military and political capacity. Under his rule the Bulgarian realm extended from the Carpathians to the neighbourhood of Adrianople; Serdica (the present Sofia) was taken, and the valley of the Struma conquered. Prêslav, the Bulgarian capital, was attacked and burned by the emperor Nicephorus, but the Greek army on its return was annihilated in one of the Balkan passes; the emperor was slain, and his skull was converted by Krum into a goblet. The reign of Boris (852-884) is memorable for the introduction of Christianity into Bulgaria. Two monks of Salonica, SS. Cyril and Methodius, are generally reverenced as the national apostles; the scene of their labours, however, was among the Slavs of Moravia, and the Bulgars were evangelized by their disciples. Boris, finding himself surrounded by Christian states, decided from political motives to abandon paganism. He was baptized in 864, the emperor Michael III. acting as his sponsor.
It was at this time that the controversies broke out which ended in the schism between the Churches of the East and West. Boris long wavered between Constantinople and Rome, but the refusal of the pope to recognize an autocephalous Bulgarian church determined him to offer his allegiance to the Greek patriarch. The decision was fraught with momentous consequences for the future of the race. The nation altered its religion in obedience to its sovereign, and some of the boyars who resisted the change paid with their lives for their fidelity to the ancient belief. The independence of the Bulgarian church was recognized by the patriarchate, a fact much dwelt upon in recent controversies. The Bulgarian primates subsequently received the title of patriarch; their see was transferred from Prêslav to Sofia, Voden and Prespa successively, and finally to Ochrida.