The emperors Probus, Constantine, Julian and Valentinian, themselves foreigners, were worn out with repulsing these repeated assaults, and the general enervation of society did the rest.
Dreams of conquests and extension had long been abandoned, and the pressing question of the time was how to repel the persistent assaults of Persia and the barbarians upon the frontiers of the realm, and so retain the dominion inherited from the valour of the past.
The size of the empire made it difficult, if not impossible, to attend to these assaults, or to control the ambition of successful generals, from one centre.
It is not strange that these fortifications defied the assaults of barbarism upon the civilized life of the world for more than a thousand years.
He held his own, despite the assaults of 1 great army gathered by Roderic the High King, and of a viking Fleet which came to help the conquered jarls of \Vaterford and Dublin.