It was in St. Leo’s pontificate that Greek and Latin Christianity were finally divorced. While Western Europe was shrouded in the darkness, misery, and ignorance of the ninth and tenth centuries, the Eastern Empire, under the Macedonian emperors (867-1057), recovered some of the territory it had lost to the Arabs, reasserted its leadership in south Italy, and experienced a new flowering of literature and art. The Greek Church drew strength and pride from the revived wealth and power of the Byzantine state, won Russia, Bulgaria, and Serbia to the Eastern observance, and resented more sharply than ever the claims of a debased and impoverished papacy to the ecclesiastical monarchy of the Christian world. To the Greeks of this age the Germans, Franks, and Anglo-Saxons of the contemporary West seemed crude barbarians, an illiterate and violent laity led by a worldly and corrupt episcopate. The papal rejection of the Byzantine emperor for the king of the Franks, the papal appropriation of the exarchate of Ravenna, the papal coronation of a rival Roman emperor, the papal drive into Greek Italy—these galling political events, and not the slight diversities of creed, severed Christendom into East and West.
In 1043 Michael Cerularius was appointed Patriarch of Constantinople. He was a man of noble birth, wide culture, keen intellect, and resolute will. Though a monk, he had risen through a political rather than an ecclesiastical career; he had been a high minister of the Empire, and would hardly have accepted the patriarchate if it had involved submission to Rome. In 1053 he circulated a Latin treatise by a Greek monk, which strongly criticized the Roman Church for enforcing clerical celibacy contrary to apostolic example and ecclesiastical tradition, for using unleavened bread in the Eucharist, and for adding filioque to the Nicene Creed. In that same year Cerularius closed all those churches in Constantinople that observed the Latin ritual, and excommunicated all clergy who should persist in its use. Leo, then at the height of his pontificate, despatched a letter to Cerularius demanding that the Patriarch should recognize the supremacy of the popes, and branding any church that refused such recognition as “an assembly of heretics, a conventicle of schismatics, a synagogue of Satan.”76 In a milder mood Leo sent legates to Constantinople to discuss with the emperor and the Patriarch the differences that kept the two branches of Christianity apart. The emperor received the legates cordially, but Cerularius denied their competence to deal with the issues. Leo died in April, 1054, and the papacy remained vacant for a year. In July the legates, taking matters into their own hands, deposited on the altar of St. Sophia a bull excommunicating Cerularius. Michael convened a council representing all Eastern Christianity; it recapitulated the grievances of the Greek against the Roman Church, including the shaving of the beard; it formally condemned the bull of the legates, and “all who had helped in drawing it up, whether by their advice or even by their prayers.”77 The schism was now complete.