1244, Llywelyn and his brothers became the heirs of their father's claims on the principality of Wales, then ruled by their uncle, Davydd ab Llywelyn [see Davydd II]. Llywelyn and his elder brother Owain (surnamed Owain Goch, that is Owain the Red) do not appear to have shared with their younger brothers, Rhodri and Davydd, the English prison, in escaping from which their father lost his life. But in March 1246 their uncle Davydd died without issue. Davydd had always been suspected from his English connections, and the Welsh nobles now joyfully turned to his nephews as full Welshmen both on their father's and mother's side, and the natural representatives of the patriotic tradition. After the local custom, and by the advice of the 'good men,' Llywelyn and Owain now made an equal division of their territories. But the English seneschal of Carmarthen seized this opportunity to take possession of the southern dependencies of the principality, then directly ruled by Maelgwn Vychan, who fled to Gwynedd and sought the protection of the two brothers. This involved the prospect of hostilities with Henry III, and on the seneschal's approach to Deganwy, Owain and Llywelyn took to the hills. A reconciliation was, however, soon effected. Llywelyn and Owain went to Woodstock and performed homage to Henry III, whereupon, on 30 April 1247, Henry signed a convention in which he pardoned them their rebellion (Fœdera, i. 267). The terms exacted testify their weakness. All the lands to the east of the Conway—including the four cantreds of Perveddwlad—went to the king. The advances of the royal officials in the south were not checked, and Maelgwn recovered only a fragment of his former heritage. Snowdon and Anglesey alone remained to the sons of Gruffydd (Worcester Annals, p. 438). It was a virtual undoing of the great work of Llywelyn ab Iorwerth. The princes of Wales were again confined to the highlands of Gwynedd.
For the next few years there was peace upon the borders. In 1248 Henry allowed Owain and Llywelyn to transfer the body of their father from the Tower to Aberconway Abbey (Brut y Tywysogion, p. 335). The princes of Gwynedd were too weak to be able to do Henry much harm, and soon quarrelled with each other. Llywelyn, though the younger, was certainly more able and energetic than Owain, and showed such an ascendency as to provoke universal jealousy among the Welsh chieftains. Owain was the first to revolt, having now the support of the younger brother, Davydd. In 1254 open war broke out between Llywelyn and his brothers. A pitched battle was fought at Bryn Derwyn, where, after an hour's hard fighting, Llywelyn prevailed. Owain Goch was taken prisoner, and remained in confinement until 1277. Davydd fled to England, leaving Llywelyn sole ruler of Gwynedd.
Llywelyn now aspired to win back for himself the position which had been attained by Llywelyn ab Iorwerth. Upon the death of his vassal, Maredudd, he took Meirionydd into his own hands. Such acts excited the alarm of the petty Welsh chieftains. The Welsh leaders in South Wales began to fear him. Gruffydd ab Gwenwynwyn [q. v.], lord of Cyveiliog or Upper Powys, sought protection from him by allying himself with the English. But more formidable to Llywelyn's power was the new departure which took place at the English court. In 1254 Henry III granted his firstborn son, Edward, on his marriage, the earldom of Chester and all the lands held by the crown in Wales. This included not only the four cantreds of Perveddwlad, but also those southern districts between the Dovey and Carmarthen Bay in which, since the times of Llywelyn ab Iorwerth, the rule of the lords of Gwynedd had gone on side by side with that of the lords-marchers and the royal officials. The bailiffs of the young earl at once wished to show his power. In 1255 they made a survey of the lands and castles in Gwynedd, aiming apparently at the subjection of the four cantreds to the jurisdiction of the palatine authorities at Chester. In 1256 the violent Geoffrey of Langley, Edward's agent in the south, strove to set up a shire system with English laws at the expense of Welsh local customs (Dunstaple Annals, p. 200; Matt. Paris, Hist. Major, v. 613). This resulted in the first faint beginnings of the counties of Carmarthen and Cardigan.
Loud complaints at once arose among the Welsh tenants, who had accepted unwillingly the rule of English lords, and, disregarding the proffered mediation of Richard of Cornwall (Matt. Paris, v. 613), Llywelyn at once championed their grievances. In 1256 he invaded Perveddwlad, spreading desolation to the gates of Chester (Bermondsey Annals, p. 461). Within a week he had subdued the whole district except the castles of Deganwy and Diserth. He next marched south to Llanbadarnvawr, the northern stronghold of the new county of Cardigan. There he boldly granted to his vassal, Maredudd ab Owain [q. v.], that part of Ceredigion which belonged to Edward, and the district of Builth, which was held by the Mortimers (Brut y Tywysogion, p. 343). He then drove his cousin, Roger Mortimer, out of Gwrthrynion, and, early in 1257, expelled