The Early Christians did not have any central administration. In fact we find the opposite.
- The first council took place in Jerusalem (Acts 15) in order to define if Gentile Christians should follow the Hebrew law of circumcision. The elders of Jerusalem, the Apostles, gathered in order to settle this matter, since Apostle Paul was facing a huge issue by the Hebrew Christians due to the fact that he was baptizing the Gentiles without circumcision.
- Apostle Paul didn't need any approval from any central Christian administration. After he converted to Christianity (at that time called Odos-The Way) he started preaching Jesus Gospel the Nations.
- In Antioch Church, they decided to change the name of Jesus followers known at that time as Odos- The Way, to Christians. Then the rest of the Christian congregations accepted their new name.
- After the end of the first council in Jerusalem, Apostle Paul proceeded with the circumcision of Timothy, actually he disobeyed the final commandments of the Council. Still there were no sanctions against him.
Christian church faced for 300 years severe persecution by the Romans, but beside the persecution Christianity survived. It was the message of the New God, who speaks about love and equality. This message was spread out due to the common Hellenic language and culture of the Roman Empire and that is why we also call the New Testament - The Greek Scriptures.
Constantine saw this new religion as a tool to unify and keep the vast Roman Empire together. The Nicea Council, although he was present, the Bishops defined Jesus substance. What was told there by the Bishops it was what was considered by the Church for the last 300 years. We have numbers of Early Church writings from various Bishops, like the Letter from Ignatius to the Church of Magnisius, around 120 A.D that clearly showed Jesus Divinity, and what did Christians held and believe.
The Church after coming out from the catacombs was finally free to build Temples to worship Jesus like the magnificent Temple Of Saint Sophia in Constantinople, the Capitol of the East Roman Empire. The symbol of the Ecumenical Patriarch was the 2 headed Eagle, pointing that the Roman Empire has West and East.
Unfortunately this unified Church came to an end at 1080A.D, when Schisma occurred with the Orthodox Apostolic Church and the Roman Catholic Church. The great issue of Filiogue still separates the East and West Church along with Infallible of Pope. At the Orthodox Church the Ecumenical Patriarch it is consider equal among the rest of the Bishops of the Church and he is only the presiding overseer of the Church, something that the Orthodox Church correctly couldn't accept Pope to be above all.
Indeed the East Roman Empire-wrongly called Byzantine by many, lasted for more than a 1000 years, from 325 A.D when Constantine moved the capitol of Roman Empire to Constantinople and ended at 1453 A.D when Ottoman Turks siege Constantinople, a city that was ready to fall due to the previous 2 Crusades that supposed to free the Holy Land, but actually they destroyed the structure of the East Roman Empire.