Celtic Orthodox Church was created in 1866.

The most important Church of the Middle Ages was the Catholic Church. When it split in 1054, it became the Roman Catholic Church in the West and the Eastern Orthodox Church in the East.

There were always other Churches. The Celtic Church, the Coptic Orthodox Church and the Oriental Orthodox Churches were very early and all predated the Middle Ages. The Celtic Christian Church was absorbed by the Catholic Church, but the others continue. There were also heterodox organizations outside orthodox Christianity, and some of these were declared heretical, in some cases resulting in military operations.

During the times of ancient Rome, there were several different Church organizations, but the largest was the Church of Rome. Others included the Celtic Church, the Coptic Orthodox Church, the Oriental Orthodox Church, and so on.

The Roman Church divided in the Great Schism of 1054 into the Roman Catholic Church and the Eastern Orthodox Church.

In addition, there were many heretical church groups. Notable of these were the Catharists, against whom the Roman Catholics launched the Albigensian Crusade. But the list of groups challenging the main Church was long.

There is an Orthodox Church and a Catholic Church. There is no Catholic Orthodox Church.

Eastern Orthodox Church (or the Christian Orthodox Church).