In the extreme west, in Dyfed, the land of fiords, Arnulf of Montgomery had early founded the Norman power, but he was involved in the fall of his brother, Robert of Bellesme, and Henry I. tried to form the land into an English shire, and planted a colony of Flemings in "Little England beyond Wales." But it was too far off for the royal power to be effectively exercised there, and the Earldom of Pembroke was granted to a branch of the De Clares, who had already conquered Ceredigion, and built castles at Cardigan and Aberystwyth. The De Clares also held Chepstow and lands in Lower Gwent. The Earldom itself was smaller than the present shire of Pembroke, and William Marshall, who succeeded the De Clares through his marriage with the daughter of Richard Strongbow (1189), owed his commanding position in English history of the thirteenth century far more to his personal qualities, his courage and wisdom and patriotism, than to his territorial possessions.
It was by driving the De Clares out of Ceredigion in Stephen's reign that Rhys ap Gruffydd laid the foundation of his power, and raised Deheubarth to be the foremost of the native principalities. The Lord Rhys was clever and farseeing enough to win the confidence of Henry II., and received from him the title of Justiciar--or King's Deputy--in South Wales. As long as Owain Gwynedd lived the unusual spectacle was seen of a prince of South Wales and a prince of North Wales working harmoniously together. But after Owain's death (1170) Rhys fought with his successors over the possession of Merioneth, while Owain Cyfeiliog, the poet-prince of Powys, did all he could to thwart him. In 1197 the death of Rhys, "the head and the shield and the strength of the South and of all Wales," and the civil wars among his sons, opened his principality again to the encroachment of foes on all sides, and removed one danger from Powys. Powys, however, was being steadily squeezed by the pressure of Gwynedd on one side, and the growing power of Mortimer on the other, and its princes resorted to a shifty diplomacy and a general adherence--open or secret as circumstances dictated--to the English Crown, till they sank at length into the position of petty feudatories of the English king.