The king of Gwynedd claimed supremacy as head over the rest, and although this was allowed as a theory, if practically asserted it always met with armed resistance. But this was not all that went to weaken the Welsh opposition. Each prince who left sons carved up his principality into portions for each, and as the brothers were mutually jealous and desirous of acquiring each other’s land, this led to incessant strife and intrigue with the enemy in the heart of each of the three principalities. A great opportunity had offered. Rhodri the Great had united all Wales in his own hands, as mentioned already. But the union lasted only for his life; all flew apart once more at his death in 877, and that just at the moment when unity was of paramount importance. Llewelyn ab Iorwerth, surnamed “the Great,” was king of Gwynedd at the beginning of the thirteenth century, and he had sufficient wit to see that the only salvation for Wales was to be found in its reunion, and he attempted to achieve this. As Powys was obstructive, he had to fight Gwenwynwyn its king, then to subject Lleyn and Merioneth. In 1202 Llewelyn was firmly established in Gwynedd, and he married Joan, the daughter of King John, who proceeded to reinstate Gwenwynwyn in Powys. In 1211 this prince sided with Llewelyn against John, who, furious at this act of ingratitude, hanged twenty-eight Welsh hostages at Nottingham. Llewelyn now turned his attention to the conquest of South Wales. He stormed one castle after another, and obtained recognition as prince of Dynevor. But in 1216 the false and fickle Gwenwynwyn abandoned the Welsh side and went over to that of the English. After some fighting Llewelyn submitted to Henry III. at Worcester in 1218. His grandson, another Llewelyn, was also an able man, but he lacked just that essential faculty of being able to detect the changes of the sky and the signs of the times, and that ruined him. In 1256 Llewelyn was engaged in war against the English. He had done homage to Henry III. in 1247, but the unrest in England caused by the feeble rule and favouritism of Henry had resulted in the revolt of the barons. Llewelyn took advantage of this condition of affairs to recover Deganwy Castle and to subdue Ceredigion. Then he drove the unpatriotic son of Gwenwynwyn out of Powys. The same year he entered South Wales, and was everywhere victorious. Brecon was brought under his rule, and the castles held by the English were taken and burned. But Llewelyn’s great difficulty lay with his own people, though his power was used for the recovery of Wales from English domination. In 1265 he had received the oaths of fealty throughout Wales, which was now once more an independent principality. But he made at this point a fatal mistake. He did not appreciate the strength and determination of Edward I., the son of the feeble Henry, and in place of making favourable terms with him he intrigued against him with some revolted barons.