d.1059. Patriarch of Constantinople. Under his direction the final severing between the Eastern and Western churches took place, often referred to as the Great Schism of 1054. Differences between Rome and Constantinople did not originate under his regime, but went back over many centuries. The patriarch brought to his office the ability to use political power to his end. Constantine Monachus, who was emperor at the time, was negotiating with Pope Leo IX concerning the defense of S Italy against the Normans. As a part of the deal the emperor of Constantinople agreed to give back the southern Italian churches to the jurisdiction of the papacy. When Patriarch Cerularius found out about these negotiations, he decided to flex his power against the weak emperor. He began by trying to force the Latin churches in Constantinople to use Greek language and practices. When they refused in the year 1052, he closed them down.
The ritual divergences which were used as the excuse for this became the focal points of the dispute. The real issues which had been dividing them and are still dividing them, such as the equation of the papacy and the, remained beneath the surface at the time of the schism. The papacy apparently got the message that Cerularius was reacting to the capitulation of the Byzantine emperor to Rome. This led to an extreme assertion of papal authority to which, of course, Cerularius reacted. When the legates came from Leo, Cerularius refused to see them-so they excommunicated him. The patriarch in turn excommunicated those who had come representing the pope. Thus the division was complete.