Let us begin by making clear what we mean by " The West. The West had not been created a separate empire by Diocletian's far-reaching reforms in the administration. It was, in his time, simply the sphere of jurisdiction of the junior of the two partners who, henceforward, were jointly to share the indivisible imperium?. This new system was only more or less preserved in the next hundred years. For thirteen years , under Constantine the Great, the Empire had but a single emperor; and after a short interval it was again united under his son Constantius II Valentinian I divided it once again in , and so it remained until the assassination of Valentinian II nearly thirty years later.
This emperor left no heir, and his eastern colleague, mastering the usurper who had murdered Valentinian, now became sole emperor of the Roman world. This was Theodosius, called the Great, destined, though he could not know it, to be the last man to rule effectively the vast heritage in which, since the days of Augustus, the lands that encircle the Mediterranean had been politically and culturally united.
Theodosius died January 28, prematurely, only a few months after his final establishment, and within ten years the forces, to ward off which the best efforts of every great mind in the last hundred years had been directed, surged up yet once again, this time to have their will. They were destined -- these forces which, carelessly and none too accurately, we have come to lump together as the Barbarian Invasions -- so to transform the West that, in the end, it became a new thing, politically and culturally.
In that long process political unity disappeared and the Western Emperor, too, who was its symbol and its source. The Catholic Church survived. To understand what this meant we need to recall how much of Catholicism there was to survive; we must survey the Catholic achievement in the West at the moment when the Barbarian Invasions began, describe the history of the Church in the West between the act of Constantine which definitely gave it legal security and the death of the last great personality whom that new age of the Christian Empire produced, St.
It is the story of Catholicism in Africa, perhaps the most Catholic province of the West, slowly shaken to pieces by the terrible experiences of the long Donatist schism; the story of Spain similarly disturbed but in less degree by the friends and the enemies of Priscillian; the story of the first attempts to evangelise what was the least Catholic part of all -- the countrysides of Gaul -- and of the Roman See's careful organisation of new means through which to develop the exercise of its traditional primacy.
