What was the structure of the roman church prior to the fifth century?

Although the church was still a single entity at the time, the split into Catholic and Orthodox came later, there was a problem that caused a smaller but a different schism. The patriarch caused problems with claims of Jesus' two natures, divine and human, which caused those who believed it to be connected to split and open their own Orthodox churches in the orient. These were places like Egypt and Persia.

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