The earls of Chester did not retain the sovereignty of Gwynedd; on the death of Rufus, Griffith ap Cynan returned, and obtained possession of Anglesea. He was favourably received at the court of Henry I., and gradually recovered possession of the whole of Gwynedd. In 1114 Henry had to undertake a great expedition against him to enforce the payment of tribute;[855] from which, and from the peaceful manner in which Griffith seems to have acquired his principality, we may infer that this tribute was the bargain of his possession. It very likely suited Henry's policy better to have a tributary Welsh prince than a too powerful earl of Chester. The reigns of the three first Norman kings were the time in which Norman supremacy in Wales made its greatest advances. With the accession of Stephen and the civil war which followed it came the great opportunity for the Welsh of throwing off the Norman yoke. Powys appears to have been the only province which remained faithful to the English allegiance, under Madoc ap Meredith.[856] The history of Norman conquest in Powys is more confused than that of Gwynedd, but Domesday shows us that Rainald, the Sheriff of Shropshire, a vassal of Earl Roger of Shrewsbury, was seated at Edeyrnion and Cynlle, two districts along the upper valley of the Dee.[857] Robert of Rhuddlan held part of his grant of "Nort Wales," namely the hundred of Arwystli, in the very centre of Wales, under Earl Roger. Professor Lloyd remarks, "Earl Roger claimed the same authority over Powys as Earl Hugh over Gwynedd, and the theory that the princes of this region were subject to the lords of Salop survived the fall of the House of Montgomery."[858] We have already spoken of Earl Roger de Montgomeri and his brood of able and unscrupulous sons.[859] The palatine earldom of Shrewsbury lay along the eastern border of central Powys, and must soon have proved a menace to that Welsh kingdom. Domesday Book shows us that Earl Roger had already planted his castle of Montgomery well within the Welsh border at that date. But the ambition of Earl Roger and his sons stretched beyond their immediate borders. It is probable that they used the upper Severn valley, which they fortified by the castle of Montgomery, and possibly by the castle of Welshpool, as their road into Ceredigion, for we find Earl Roger named by the _Brut_ as the builder of the castle of Cilgerran,[860] and some say of Cardigan also. Possibly he was helping his son Arnolf in the conquest of Pembroke. In 1098 we find his successor, Earl Hugh, allied with the Earl of Chester in the invasion of Anglesea.