Church, which supported the ruling classes of the country and lent them authority at the same time that it increased its own, was antipathetic to the Slavs, and the Bogomil heresy drew much strength from its nationalistic colouring and from the appeal which it made to the character of the Balkan Slavs, who have always been intolerant of government by the Church.  But neither the civil nor the ecclesiastical authorities were able to cope with the problem; indeed they were apt to minimize its importance, and the heresy was never eradicated till the arrival on the scene of Islam, which proved as attractive to the schismatics as the well-regulated Orthodox Church had been the reverse.

The third quarter of the tenth century witnessed a great recrudescence of the power of Constantinople under the Emperor Nikiphoros Phokas, who wrested Cyprus and Crete from the Arabs and inaugurated an era of prosperity for the eastern empire, giving it a new lease of vigorous and combative life.  Wishing to reassert the Greek supremacy in the Balkan peninsula his first act was to refuse any further payment of tribute to the Bulgarians as from 966; his next was to initiate a campaign against them, but in order to make his own success in this enterprise less costly and more assured he secured the co-operation of the Russians under Svyatoslav, Prince of Kiev; this potentate’s mother Olga had visited Constantinople in 957 and been baptized (though her son and the bulk of the population were still ardent heathens), and commercial intercourse between Russia and Constantinople by means of the Dnieper and the Black Sea was at that time lively.  Svyatoslav did not want pressing, and arriving with an army of 10,000 men in boats, overcame northern Bulgaria in a few days (967); they were helped by Shishman and the western Bulgars, who did not mind at what price Peter and the eastern Bulgars were crushed.  Svyatoslav was recalled to Russia in 968 to defend his home from attacks by the Tartar Pechenegs, but that done, he made up his mind to return to Bulgaria, lured by its riches and by the hope of the eventual possession of Constantinople.

The Emperor Nikiphoros was by now aware of the danger he had imprudently conjured up, and made a futile alliance with eastern Bulgaria; but in January 969 Peter of Bulgaria died, and in December of the same year Nikiphoros was murdered by the ambitious Armenian John Tzimisces,[1] who thereupon became emperor.  Svyatoslav, seeing the field clear of his enemies, returned in 970, and in March of that year sacked and occupied Philippopolis.  The Emperor John Tzimisces, who was even abler both as general and as diplomat than his predecessor, quietly pushed forward his warlike preparations, and did not meet the Russians till the autumn, when he completely defeated them at Arcadiopolis (the modern Lule-Burgas).  The Russians retired north of the Balkan range, but the Greeks followed them.  John Tzimisces besieged them in the capital