Upon the death of Nikephoros, Sviatoslav decided to make war on Bulgaria for his own aggrandizement, and in 969 he captured Boris, carrying him as far east as Philippopolis. Here the Greek Emperor, Zinisces, the successor of Nikephoros, with the help of the defeated Bulgarians themselves, drove the Northmen back. Sviatoslav was compelled to seek refuge in Silistria, where he sustained a siege of three months. After his final capture he was liberated and allowed to return to his native land, but, while on the march, he and his few surviving adherents were ruthlessly slain by a marauding band of hostile tribesmen. [Illustration: THE SAINT CRAL CATHEDRAL, SOPHIA.] This may be said to have been the first Russian invasion of Bulgaria, the direct result of which was the fusion of the Northern and the Southern Slavs. Bulgarian history proper begins, however, with the nation’s conversion to Christianity under the Tzar Boris, late in the ninth century. About the same time the Cyrillic alphabet—now adopted by all Slav peoples, including the Russians—was introduced by the great apostles, Cyril and Methodius. Under Assen, Bulgaria, then belonging to Greece, revolted, conquered, and Assen I, the founder of the Assenide dynasty, was chosen Tzar. This dynasty reached its height under Assen II (1218-1241) and a century later the country fell under Servian rule; to its advantage, however, for King Dushan of Servia proved himself a wise and jealous protector. After the death of King Dushan, the Northern provinces of the Balkan Peninsula commenced to feel the effects of Turkish invasions. For some years the Bulgarians defended their lives and their property heroically; but, finally, Tzar Shishman III, having been deserted by his allies, surrendered and acknowledged himself a subject of Sultan Murad I. Not, however, until after the bloody battle of Kossovo in 1389 was Bulgaria brought completely under Ottoman rule. For the following five hundred years the Turks pillaged and sacked the country and outraged its inhabitants. Europe remained in ignorance of the atrocities, for her mind was distracted by her own sanguinary wars. The Ottoman domination and tyranny was social as well as political; it was felt keenly, not only in manners and morals, but in social liberty also. Nevertheless, it is a singular fact that no determined attempt to assimilate Bulgaria, as a whole, to Turkish customs and Mohammedanism was made during all these years. The only instances of religious coercion were prevalent in the cases of young Bulgarian girls who had been snatched from their very doorsteps and placed in the harem of some bigoted Pasha.