Then the Moravians rose against the Franks, under a man named Slavomir, who, according to one story, was a pupil of Methodius. The Emperor thereupon set Svatopluk free, and sent him at the head of an army to suppress the new rising. Svatopluk betrayed his soldiers to his countrymen, destroyed the German army, and once more became Duke of Moravia. He now felt it impossible any longer to pose as the champion of the German party; and he had married the sister of Duke Bor̆ivoj, of Bohemia, in order to strengthen the alliance of the Slavs against the Franks. As a part of his new policy, he was forced, for a time, to encourage the movement of Methodius; and it was during this period that the archbishop or one of his followers converted and baptised Bor̆ivoj, and induced him to found two churches in memory of St. Clement of Rome, whose remains Cyril had discovered in his expedition to the Chazars.
There seems some difficulty in ascertaining how far the Slavonic ritual came into general use in Bohemia at this time. It is tolerably certain, on the one hand, that Methodius did not desire to oppose the authority of the Bishop of Regensburg, who claimed to be primate over the Bohemian Christians; and that bishop, like all the German prelates, was opposed to the spread of the Slavonic ritual. On the other hand, it is clear that, as Christianity grew in Bohemia, it connected itself with Slavonic traditions; and we find that in less than a century from this time the Bohemian congregations had adopted a Slavonic hymn as a necessary part of their ritual.
But, however slow the progress of Slavonic Christianity may have been in Bohemia, Methodius does not seem to have excited there that savage hostility which he continued to provoke in Moravia. Svatopluk and his courtiers were, no doubt, indignant at the higher morality preached by Methodius; and one of the claimants of the German Empire, with whom Svatopluk was alternately in alliance and enmity, resented extremely the authority claimed by Methodius over Pannonia as well as Moravia. But, in order to strengthen their position, the opponents of Methodius took advantage of his having come from Constantinople, to attack him as a rebel against the Pope, and a supporter of the Greek heresy of the Single Procession.