Throughout this troubled age the causes of confusion were twofold. On the one hand the Empire itself was so vast and scattered that it tended now to fall to pieces of its own momentum, as the seedbox opens to scatter its seeds. Britain, Gaul, Germany, Palmyra--each in its turn began to feel a unity of its own. Rome was far away, and the government was often weak and negligent. Here was an opportunity for the local generals to carve out thrones for themselves. While the emperor hurried this way and that fresh rebellions broke out in his rear. It was no one’s fault in particular. The world-state was impossible in theory as in practice. It was only possible while the provinces were barbarian. When they became civilised and self-conscious they were bound to feel their natural unity. In the second place, the barbarians were now grown to full stature. They were no longer quarrelsome tribes which could be turned against one another by adroit statecraft, but nations much less barbarous than of old, with some organisation and a purpose above that of mere plunder. No artificial ramparts could hold them. It is very doubtful whether even the legions of Rome at their best could have resisted these repeated assaults on all sides. The first great inroad across the Danube took place in the reign of M. Aurelius. It was crushed, as the column of that emperor depicts, and Sarmatia and Marcomannia were added as short-lived provinces. It is in the third century that we begin to hear of the greater barbarian nations, or groups of tribes, of the Alemanni and the Suevi, the Franks, the Saxons, the Goths, and the Vandals. Battle after battle was fought and triumph after triumph won against them, but they still pressed on. The weaker emperors essayed to buy them with gold, the wiser with land, the craftier set them to slay one another, but still they moved forward resistlessly, wave after wave, like the sea. This again was nobody’s fault. It may have been the movement of Tartar savages in the Far East which set the Wandering of the Nations in motion. Whatever it was, all eastern and northern Europe was seething with restless movement and the tide rolled on irresistibly against the bulwarks of civilisation. Triumphs as great and glorious as those of Scipio and Marius were gained by Roman armies even in the fourth century. But the enemy was ubiquitous, the task impossible.