In 1054 papal legate, Cardinal Humbert, marched into the Orthodox Cathedral of Hagia Sophia in Constantinople and banged a bull of excommunication onto the altar before the ecumenical patriarch, Michael Cerularius. This formalized the split between the Catholic and Orthodox churches that has persisted, despite a brief reunion, for nearly a millennium.
Split Between Catholic and Orthodox – Long in the Making
It is erroneous to think that the split just happened. Constantine had established a Christian church across his empire. The fate of that church was linked to the fate of the empire: as the Roman world split between Latin and Greek divisions, the tectonic crack between two churches grew. The trouble was rooted in political structures and language differences.
The Roman Empire survived in the Greek East, whereas the West fell under the control of Germanic warlords who had flooded into Europe as imperial power failed. The West emphasized Latin, whereas the East spoke Greek. As society broke down in the fierce struggles that followed imperial collapse, many on each side failed to learn the language of the other. While there was some competence on each side, there was little scholarly expertise. This meant that misunderstandings could occur, especially when dealing with complex theological documents.
Part of the trouble was the status of the papacy. The church was ruled by apostolic sees, bishoprics deemed to have been founded by apostles and therefore sure repositories of the apostolic tradition. Each was governed by a patriarch/pope. These included Rome, where Peter and Paul had settled, Constantinople [dubiously connected with Andrew], Alexandria and Antioch.
The Bishop of Rome was supposed to be first among equals, presiding over the other patriarchs in fraternal relationship. Decisions on doctrine were made by ecumenical councils, in which the collected bishops met to discuss doctrinal matters. As time passed, however, the orthodox sensed that the popes regarded themselves as emperors over all the others, and were becoming more domineering. Trouble came when the popes started making doctrinal decisions on their own without ecumenical councils, inserting words into the creed without conciliar approval.