The Cambridge Medieval History - Book IV: The Fall of the Western Roman Empire

This process of history may be said to have entered on its effective stage in the West with Alaric's invasion of Italy. But it had been present, as a potentiality and a menace, for many years before Alaric heard the voice that drew him steadily towards Rome. The frontier war along the limes was as old as the second century. The pressure of the population of the German forests upon the Roman world was so ancient and inveterate, and so much of that population had in one way or another entered...