[RobbyS]

Given that the Emperor Constantine exercised the role of "outside bishop," in what amounted to a Greek synod, and that his successors in Constantinople played also played such a role, one might say that the Byzantine tradition began at this time.

[The_Reader_David]

I think you will find that St. Constantine Equal-to-the-Apostles did not actually play any role at Nicea except to see that the proceedings of the Council were orderly. There is good evidence that he personally had Arian leanings--in particular the court chaplain who finally baptized him was an Arian--but accepted the condemnation of Arius as the word of Christ's Church. An Emperor did indeed call each of the Holy Ecumenical Councils (the Seven acknowledged by both us and the Latins, and the two they don't recognize--and their "Eighth" as well). Nothing exceptional there: after all God did wait until His people Israel had been incorporated into a large, stable, and linguistically more-or-less homogeneous empire before becoming Incarnate for our salvation. Doubtless because He wanted to use the Empire to further our salvation once the necessary compenent of if had been accomplished by Christ's Incarnation, Crucifixion, and Resurrection and the descent of the Holy Spirit.