In ecclesiastical matters also the differences were of long standing. These related to questions of jurisdiction between the two patriarchates. Up to the eighth century, the patriarchate of the West included a number of provinces on the eastern side of the Adriatic--Illyricum, Dacia, Macedonia, and Greece. But Leo the Isaurian, who probably foresaw that Italy would ere long cease to form part of his dominions, and was unwilling that these important territories should own spiritual allegiance to one who was not his subject, altered this arrangement, and transferred the jurisdiction over them to the Patriarch of Constantinople. Against this measure the bishops of Rome did not fail to protest, and demands for their restoration were made up to the time of the final schism. A further ecclesiastical question, which in part depended on this, was that of the Church of the Bulgarians. The prince Bogoris had swayed to and fro in his inclinations between the two churches, and had ultimately given his allegiance to that of the East; but the controversy did not end there. According to the ancient territorial arrangement the Danubian provinces were made subject to the archbishopric of Thessalonica, and that city was included within the Western patriarchate; and on this ground Bulgaria was claimed by the Roman see as falling within that area. The matter was several times pressed on the attention of the Greek Church, especially on the occasion of the council held at Constantinople in 879, but in vain. The Eastern prelates replied evasively, saying that to determine the boundaries of dioceses was a matter which belonged to the sovereign. The Emperor, for his part, had good reason for not yielding, for by so doing he would not only have admitted into a neighboring country an agency which would soon have been employed for political purposes to his disadvantage, but would have justified the assumption on which the demand rested, viz., that the pope had a right to claim the provinces which his predecessors had lost. Thus this point of difference also remained open, as a source of irritation between the two churches. But behind these questions another of far greater magnitude was coming into view, that of the papal supremacy. From being in the first instance the head of the Christian church in the old Imperial city, and afterward Patriarch of the West, and _primus inter pares_ in relation to the other spiritual heads of Christendom, the bishop of Rome had gradually claimed, on the strength of his occupying the _cathedra Petri_, a position which approximated more and more to that of supremacy over the whole Church. This claim had never been admitted in the East, but the appeals which were made from Constantinople to his judgment and authority, both at the time of the iconoclastic controversy and subsequently, lent some countenance to its validity.