A frontier has been called "an area inviting entrance." For the Norman invaders of England the Welsh peninsula was such an area. Fertile forested lowlands invited agricultural occupation; a fierce but primitive and disunited native population was scarcely a formidable deterrent. In The Normans in South Wales, Lynn H. Nelson provides a comprehensive history of the century during which the Normans accomplished this occupation. Skillfully he combines facts and statistics gleaned from a variety of original sources-The Anglo-Saxon Chronicle, the Domesday Book, Church records, charters of the kings and of the marcher lords, and more imaginative literary sources such as the chanson de geste and the frontier epic-to give a vivid picture of a century of strife. He describes the fluctuating conflict between Norman invaders in the lowlands and Welsh tribesmen in the highlands; the hard struggle of medieval frontiersmen to take from the new land a profit commensurate with their labors; the development of a Cambro-Norman society distinct and quite different from the Anglo-Norman culture which engendered it; and the attempt of the frontiersman to prevent the Anglo-Norman authorities from taking control of the lands he had won. The turbulent Welsh tribes provided an ever present harassment along the frontier, and Nelson begins his presentation with an account of the failure of the Saxons to control them. He examines the methods adopted by William the Conqueror to cope with the problem-the creation of the great marcher lordships and the subsequent problems in controlling these lordships-and the weakness of some Anglo-Norman kings and the strength of others. By 1171 the conquest of the Welsh frontier was complete; but as Nelson points out, this conquest was strangely limited. The frontier, which extended throughout the lowlands of Wales, stopped at the 600-foot contour line in the mountains. In his final chapter Nelson speculates upon the curious fact that large areas of seemingly inviting moorlands lying above this line remained closed to the Cambro-Norman, and his speculations lead him to some interesting inferences about the nature of the frontier's influence upon the civilization which moves in to occupy it.