Thereafter, the strength of its monarchy was what rendered England unique in medieval Europe. Three great kings in especial contributed, by their ability and indomitable power of will, to this result—William the Conqueror, Henry Beauclerk, and Henry Plantagenet. In a sense, the work of all three was the same, namely, to build up the central authority against the disintegrating effects of feudal anarchy; but the policy of each was necessarily modified by changing times and needs. The foundations of the whole were laid by the Conqueror, whose character and circumstances combined to afford him an opportunity unparalleled in history. The difficulties of his task, and the methods by which he carried it to a successful issue, are best understood in relation to the nature of the opposition he had to dread. Feudalism was the great current of the age—a tide formed by many converging streams, all flowing in the same direction, unreasoning like the blind powers of Nature, carrying away and submerging every obstacle in its path. In other parts of Europe—in Germany, France, and Italy, as in Scotland—the ablest monarchs found their thrones undermined by this feudal current. In England alone the monarchy made headway against the flood. William I. wisely refrained from any mad attempt to stay the torrent; but, while accepting it, he quietly subjected it to his own purposes. He carefully watched and modified the tendencies making for feudalism, which he found in England on his arrival, and he profoundly altered the feudal usages and rights which his followers transplanted from the Norman soil. The special expedients used by him for this purpose are well known, and are all closely connected with his crafty policy of balancing the Anglo-Saxon basis of his rule against the imported Norman superstructure, and of selecting at his own discretion such elements as suited him in either. He encouraged the adoption or intensification in England of feudalism, considered as a system of land tenure and as a system of social distinctions based on the possession of land; but he successfully endeavoured to check the evils of its unrestrained growth in its other equally important aspects, namely, as a system of local government seeking to be independent of the Crown, and as a system of jurisdiction. As a political system, it was always a subject of suspicion to William, for he viewed it in the light of his double experience in Normandy as feudal lord and feudal vassal.