The central idea of the period with which we are to deal is unity. Up till the fifth century, till the Council of Chalcedon (451) completed the primary definition of the orthodox Christian faith in the person of the Lord Jesus Christ, Christians were striving for conversion, organisation, definition. All these aims still remained, but in less prominence. The Church's order was completed, the Church's creed was practically fixed, and the dominant nations in Europe had owned the name of Christ. There remained a new and severe test. Would the {3} Church win the new barbarian conquerors as she had won the old imperial power? There was to be a great epoch of missionary energy. But of the firm solidity of the Church there could be no doubt. Heresies had torn from her side tribes and even nations who had once belonged to her fold. But still unity was triumphant in idea; and it was into the Catholic unity of the visible Church that the new nations were to be invited to enter. S. Augustine's grand idea of the City of God had really triumphed, before the fifth century was half passed, over the heathen conceptions of political rule. The Church, in spite of the tendency to separate already visible in East and West, was truly one; and that unity was represented also in the Christian Empire. "At the end of the fifth century the only Christian countries outside the limits of the Empire were Ireland and Armenia, and Armenia, maintaining a precarious existence beside the great Persian monarchy of the Sassanid kings, had been for a long time virtually dependent on the Roman power." [1] Politically, while tyrants rise and fall, and barbarian hosts, the continuance of the Wandering of the Nations, sweep across the stage, we are struck above all by the significant fact which Mr. Freeman (_Western Europe in the Fifth Century_) knew so well how to make emphatic:--"The wonderful thing is how often the Empire came together again. What strikes us at every step in the tangled history of these times is the wonderful life which the Roman name and the Roman Power still kept when it was thus attacked on every side from without and torn in pieces in every quarter from within." And the reason for this indubitably was that the {4} Empire had now another organisation to support it, based on the same idea of central unity. One Church stood beside one Empire, and became year by year even more certain, more perfect, as well as more strong. In the West the papal power rose as the imperial decayed, and before long came near to replacing it. In the East, where the name and tradition of old Rome was always preserved in the imperial government, the Church remained in that immemorial steadfastness to the orthodox faith which was a bond of unity such as no other idea could possibly supply. In the educational work which the emperor had to undertake in regard to the tribes which one by one accepted their sway, the Christian Church was their greatest support.