The First Great Council of the Church, at Nicea in 325, must have been an awesome sight to behold. The emperor Constantine called for the gathering of bishops from all parts of the Empire for the most part to deal with the teaching of Arius (that Jesus was not pre-existent and that he was the first created being). Some of these bishops had recently been imprisoned, tortured or exiled and bore on their bodies the physical marks of their faithfulness. Here at Nicea, for the first time, they had before their eyes physical evidence of the universality of the church.
Eusebius describes it in his work Life of Constantine(3.7):
There were gathered the most distinguished ministers of God, from the many churches in Europe, Libya and Asia. A single house of prayer, as if enlarged by God, sheltered Syrians and Cilicians, Phoenicians and Arabs, delegates from Palestine and from Egypt, Theban and Libyans, together with those from Mesopotamia. There was also a Persian bishop, and a Scythian was not lacking. Pontus, Galatia, Pamphylia, Cappadocia, Asia, and Phrygia sent there most outstanding bishops, jointly with those from the remotest areas of Thrace, Macedonia, Achaia and Epirus. Even from Spain…The bishop of…[Rome]…was represented by his presbyters…
This was a great universal gathering of believers who just had recently been allowed the freedom to gather together and discuss the importance of true doctrine and the nature of Christ. This would set the tone for orthodoxy for some years to come (although the battle over Arianism would not end for almost 60 years after the council).