text:  What gave in the third and fourth centuries so prodigious an impulse to the northern nations and enabled them after being so long repelled by the arms of Rome finally to prevail over it? What still more so completely paralysed the strength of the empire during that period and produced that astonishing weakness in the ancient conquerors of the world which rendered them the easy prey of those whom they had so often subdued? The ancient writers content themselves with saying that the people became corrupted; that they lost their military courage; that the recruiting of the legions in the free inhabitants of the empire became impossible; and that the semi-barbarous tribes on the frontier could not be relied on to uphold its fortunes