sentences:  It very well may have been implicit in the power granted the earldoms that they were to attack Wales, and, indeed, they did, beginning with south-east Wales, where many of the previous rebellions against England had begun.By the time of FitzOsbern's death in 1071, a castle had been established at the mouth of the Wye, and it served as a base from which the Normans continued to expand westward into Wales, establishing a castle at Caerleon by 1086 and extinguishing the Welsh Kingdom of Gwent.However, the attacks in south-east Wales ""faltered badly when [the earl of Hereford’s] son [Roger de Breteuil]... forfeited his estates for treason in 1075 and involved some of his vassals on the Welsh frontier in his downfall"".