The reign of Augustus inaugurated a uniquely long period of peace and prosperity in the history of Europe. Augustus and his successors provided for stable borders. The army and the Roman elite cooperated to insure that there was a relatively peaceful transmission of power from one emperor to the next. Moreover, the barbarian tribes on the borders were unable to mount a successful challenge to the Roman peace. By the middle of the 3rd century, this equilibrium had broken down. Internally, Roman emperors were made and unmade by their armies, and barbarians invaded often and deeply into the empire. Indeed, some of the more exposed parts of the Empire were abandoned altogether. Though there is no consensus among historians about how to weigh the many factors that brought on the Crisis, it is reasonably clear that that barbarian pressure was increasing on the frontier and did so just at a time when the Augustan settlement was breaking down before a coalition of ambitious generals and their uncivil soldiers. However one assesses the factors, the results were clear: the turmoil of foreign invasion and civil war had a profound affect on the prosperity of the cities of the Roman Empire.