As I have just said, Theodoric the Ostrogoth, like almost all the great Teutonic swarm-leaders, like Alaric the Visigoth, like Gaiseric the Vandal, like Gundobad the Burgundian, was an Arian. On the other hand, the Emperors, Zeno, for instance, and Anastasius, and the great majority of the population of Italy and of the provinces of the Empire, were Catholic. What was the amount of theological divergence which was conveyed by these terms Arian and Catholic, or to speak more judicially (for the Arians averred that they were the true Catholics and that their opponents were heretics) Arian and Athanasian? As this is not the place for a disquisition on disputed points of theology, it is sufficient to say that, while the Athanasian held for truth the whole of the Nicene Creed, the Arian--at least that type of Arian with whom we are here concerned--would, in that part which relates to the Son of God, leave out the words "being of one substance with the Father", and would substitute for them "being like unto the Father in such manner as the Scriptures declare". He would also have refused to repeat the words which assert the Godhead of the Holy Spirit. These were important differences, but it will be seen at once that they were not so broad as those which now generally separate "orthodox" from "heterodox" theologians.
The reasons which led the barbarian invaders of the Empire to accept the Arian form of Christianity are not yet fully disclosed to us. The cause could not be an uncultured people's preference for a simple faith, for the Arian champions were at least as subtle and technical in their theology as the Athanasian, and often surpassed them in these qualities. It is possible that some remembrances of the mythology handed down to them by their fathers made them willing to accept a subordinate Christ, a spiritualised "Balder the Beautiful", divine yet subject to death, standing as it were upon the steps of his father's throne, rather than the dogma, too highly spiritualised for their apprehension, of One God in Three Persons. But probably the chief cause of the Arianism of the German invaders was the fact that the Empire itself was to a great extent Arian when they were in friendly relations with it, and were accepting both religion and civilisation at its hands, in the middle years of the fourth century.