Charles the Great subjugated the Moravians, directed the Bishop of Passau to establish a mission among them, secured the conversion of their chief, Moymir, and founded the bishoprics of Olmütz and Nitra. Louis the German deposed Moymir on suspicion of treason and elevated Radislaw to power, but he soon turned against his benefactor and defeated him, formed an independent Slavic kingdom on the eastern boundary of Germany, and sent for Greek missionaries, two of whom, Cyrillus and Methodius, brothers and educated monks, were sent by the Greek Emperor Michael III. in 863.[254:2] Cyrillus understood the Slavic tongue and invented an alphabet and translated the liturgy into Slavic. He preached and celebrated service in the language of the people, and had a most able assistant in Methodius. They were very successful in their labours and built up a national Slavic Church. The German priests who had been labouring there for some time were driven out, and with them disappeared the Latin liturgy. Seeing their great success, Pope Nicholas I., in 868, invited them to Rome and won them to a friendly arrangement. There Cyrillus died in 869 but Methodius was returned as the Roman Archbishop of Pannonia. The Pope agreed both to the use of Slavic in the mass and to the independence of the Slavic Church under papal control. Ten years later Methodius made a second visit to Rome and a second agreement was entered into, satisfactory to both Rome and Moravia. He died before the ninth century ended, and before the close of the tenth century the Latin Church had replaced the Slavic. The expelled Slavic priests fled to Bulgaria to build up a new Church. Neither Charles the Great, nor his son Louis, was able to conquer the Bohemians. When Bohemia became a dependency of Moravia, however, the way was opened for the introduction of Christianity. The Bohemian Duke Borziway and his family were converted, but reaction followed under Boleslav the Cruel. Otto I. in 950 completely defeated Boleslav, recalled the priests, and rebuilt the churches. The bishopric of Prague was established in 973, and under Archbishop Severus (1083) general laws were enforced concerning Christian marriage, observance of the Sabbath, and morality. The Latin language and the Roman ritual prevailed in the Bohemian Church.[255:1] The first missionaries to Poland were Slavic, perhaps Cyrillus and Methodius. With the break-up of the Moravian kingdom, many nobles and priests fled to Poland and were kindly received. In 965 a Bohemian princess married Duke Mieczyslav and took priests with her. The Duke was converted and baptised and paganism was destroyed by force. The Church was then organised on the Latin-German model, and German priests were introduced. The first Polish bishopric was established at Posen subject to the Archbishop of Magdeburg. But it was to take many additional years before Roman Christianity was firmly established.