"Wales was under his sway, and he built castles therein," says the _Anglo-Saxon Chronicle_, in summing up the reign of the Conqueror; a passage which is scarcely consistent with its previous almost complete silence about events in Wales. There can be little doubt that William aimed at a complete conquest of Wales, and that the policy he adopted was the creation of great earldoms along the Welsh border, endowed with special privileges, one of which was the right of conquering whatever they could from the Welsh.[835] To these earldoms he appointed some of his strongest men, men little troubled by scruples of justice or mercy, but capable leaders in war or diplomacy. It was an essential part of the plan that every conquest should be secured by the building of castles, just as had been done in England. And we have now to trace very briefly the outline of Norman conquest in Wales by the castles which they have left behind them. We shall confine ourselves to those castles which are mentioned in the _Brut y Tywysogion_, the _Pipe Rolls_, or other trustworthy documents between 1066 and 1216, the end of King John's reign. Of many of these castles only the earthworks remain; of many others the original plan, exactly similar to that of the early castles of Normandy and France, is still to be traced, though masked by the masonry of a later age. Grose remarked but could not explain the fact that we continually read of the castles of the Marches being burnt and utterly destroyed, and a few months later we find them again standing and in working order. This can only, but easily, be explained when we understand that they were wooden castles built on mottes, quickly restored after a complete destruction of the wooden buildings. North Wales appears to have been the earliest conquest of the Normans, though not the most lasting. North Wales comprised the Welsh kingdoms of Gwynedd and Powys. Gwynedd covered the present shires of Anglesea, Carnarvon, and Merioneth, and the mountainous districts round Snowdon.[836] Powys stretched from the estuary of the Dee to the upper course of the Wye, and roughly included Flint, Denbigh, Montgomery, and Radnor shires. Hugh of Avranches, Earl of Chester, was the great instrument of Norman conquest in Gwynedd, and in the northern part of Powys, which lay so near his own dominions. He was evidently a man in whose ability William had great confidence, as he removed him from Tutbury to the more difficult and dangerous position of Chester, and gave his earldom palatine privileges; all the land in Cheshire was held under the earl, and he was a sort of little king in his county.