From the time of the Servian constitution downward, the change in the army had kept pace with the acceleration of movement which caused the economic competition that centralized the State. Rome owed her triumphs over Hannibal and Pyrrhus to the valour of her infantry, rather than to the genius of her generals; but from Marius the census ceased to be the basis of recruitment, and the rich refused to serve in the ranks. This was equivalent in itself to a social revolution; for, from the moment when the wealthy succeeded in withdrawing themselves from service, and the poor saw in it a trade, the citizen ceased to be a soldier, and the soldier became a mercenary. From that time the army could be used for “all purposes, provided that they could count on their pay and their booty.”[67] The administration of Augustus organized the permanent police, which replaced the mercenaries of the civil wars, and this machine was the greatest triumph and the crowning glory of capital. Dio Cassius has described how the last vestige of an Italian army passed away. Up to the time of Severus it had been customary to recruit the Prætorians either from Italy itself, from Spain, Macedonia, or other neighbouring countries, whose population had some affinity with that of Latium. Severus, after the treachery of the guard to Pertinax, disbanded it, and reorganized a corps selected from the bravest soldiers of the legions. These men were a horde of barbarians, repulsive to Italians in their habits, and terrible to look upon.[68] Thus a body of wage-earners, drawn from the ends of the earth, was made cohesive by money. For more than four hundred years this corps of hirelings crushed revolt within the Empire, and regulated the injection of fresh blood from without, with perfect promptitude and precision; nor did it fail in its functions while the money which vitalized it lasted. But a time came when the suction of the usurers so wasted the life of the community that the stream of bullion ceased to flow from the capital to the frontiers; then, as the sustaining force failed, the line of troops along the Danube and the Rhine was drawn out until it broke, and the barbarians poured in unchecked. The so-called invasions were not conquests, for they were not necessarily hostile; they were only the logical conclusion of a process which had been going on since Trajan. When the power to control the German emigration decayed, it flowed freely into the provinces. By the year 400 disintegration was far advanced; the Empire was crumbling, not because it was corrupt or degenerate, but because the most martial and energetic race the world had ever seen had been so thoroughly exterminated by men of the economic type of mind, that petty bands of sorry adventurers might rove whither they would, on what had once been Roman soil, without meeting an enemy capable of facing them, save other adventurers like themselves. Goths, not Romans, defeated Attila at Châlons.