THE idea of papal sovereignty was foreign to the Byzantines. They had trouble enough trying to understand the Western interpretation of papal primacy. Papal ‘sovereignty’ was beyond them, unintelligible, unreasonable, and unhistorical. It is true that the East Roman Christians, whom for convenience we call Byzantines, did not all live in one generation. Their cultural and political roots were in Constantinople, the ancient Byzantium; and their empire endured in one form or another for 1,100 years, from the fourth to the fifteenth centuries. In so long a span their ideas naturally evolved and changed, as did their society. But their concept of the order of the Christian world remained stable. It was based upon the formula devised by the first Christian historian, Eusebius of Caesarea, in the fourth century. The formula was an amalgam of pre-Christian, Hellenistic notions of monarchy, with Old and New Testament elements. The Christian Roman Emperor was the elect of God and, as God’s vice-gerent on earth, he ruled over what was the terrestrial reflection, albeit a poor copy, of the Kingdom of Heaven. His patriarchs or supreme bishops of the Christian Empire, especially the Patriarch of Constantinople, his capital city, were the spiritual heads of the Christian world, acting in harmony with him. Church and State were therefore one, indissoluble and interdependent.