condemned the Latin filioque clause concerning the procession of the Holy Spirit. The conflict over the patriarchal throne and supreme authority within the church was exacerbated by the success of the active missionary efforts launched by Photios. Under the guidance of Patriarch Photios, Michael sponsored the mission of Saints Cyril and Methodios to the Khazar Khagan in an effort to stop the expansion of Judaism among the Khazars. Although this mission was a failure, their next mission in 863 secured the conversion of Great Moravia and devised the Glagolitic alphabet for writing in Slavonic, thus allowing Slavic-speaking peoples to approach conversion to Orthodox Christianity through their own rather than an alien tongue. Fearing the potential conversion of Boris I of Bulgaria to Christianity under Frankish influence, Michael III and the Caesar Bardas invaded Bulgaria, imposing the conversion of Boris according to the Byzantine rite as part of the peace settlement in 864. Michael III stood as sponsor, by proxy, for Boris at his baptism. Boris took the additional name of Michael at the ceremony. The Byzantines also allowed the Bulgarians to reclaim the contested border region of Zagora. The conversion of the Bulgarians has been evaluated as one of the greatest cultural and political achievements of the Byzantine Empire. Rise of Basil the Macedonian and assassination of Michael Michael III's marriage with Eudokia Dekapolitissa was childless, but the emperor did not want to risk a scandal by attempting to marry his mistress Eudokia Ingerina, daughter of the Varangian (Norse) imperial guard Inger. The solution he chose was to have Ingerina marry his favorite courtier and chamberlain Basil the Macedonian. While Michael carried on his relationship with Ingerina, Basil was kept satisfied with the emperor's sister Thekla, whom her brother retrieved from a monastery. Basil gained increasing influence over Michael, and in April 866 he convinced the emperor that the Caesar Bardas was conspiring against him and was duly allowed to murder Bardas. Now without serious rivals, Basil was crowned co-emperor on 26 May 866 and was adopted by the much younger Michael III. This curious development may have been intended to legitimize the eventual succession to the throne of Eudokia Ingerina's son Leo, who was widely believed to be Michael's son. Michael celebrated the birth of Leo with public chariot races, a sport he enthusiastically patronized and participated in. If ensuring Leo's legitimacy had been Michael's plan, it backfired. Ostensibly