1217 his ally Reginald de Braose reconciled himself with the partisans of the young king, the Welsh subjects of the house of Braose rebelled and Llywelyn came to their help and attacked Brecon. Llywelyn forced Reginald to make his submission and then led his army over the mountains to Gower, whence he marched against the 'Flemings of Dyved,' the subjects of William Marshal, earl of Pembroke and regent of England. Llywelyn now blockaded Haverfordwest, but peace was arranged through the Bishop of St. Davids, and Llywelyn withdrew to Gwynedd with twenty of the noblest hostages of Rhos and Pembroke (ib. p. 302). In 1218 Carmarthen and Aberteivi (Cardigan) were put under the custody of Llywelyn (ib. p. 303).
After the withdrawal of Louis of France, the regent Pembroke demanded that Llywelyn should perform the homage due to the young king. In March 1218 Llywelyn and his principal nobles appeared under safe-conducts at Worcester and duly submitted themselves to their overlord (Fœdera, i. 150). Llywelyn was ordered to restore the lands of some of the king's servants, and in return was put in possession of his English estates (ib. i. 151). In 1219 there were many councils between Llywelyn and some of the English barons, but Llywelyn's cunning, says the English annalist, always saved him (Flor. Hist. ii. 170). On 4 May 1220 he held another interview with the young king at Shrewsbury, where his son Davydd [see Davydd II] was taken under the protection of his royal uncle (Fœdera, i. 159). But there were disputes as to the extent of the royal rights over Melenydd, which Llywelyn was forced to surrender, and no good result sprang from the conference (Royal Letters, i. 113, 122: cf. Eyton, Shropshire, iv. 213). In the summer of the same year a private war of unusual magnitude and importance broke out between Llywelyn and the younger William Marshal, earl of Pembroke since his father's death in 1219. Llywelyn cunningly prepared for this by getting help from the king in order to put down some rebels against the royal authority in the south. In August he suddenly burst into Pembrokeshire, capturing three castles and cruelly devastating the whole province, his pretext being the marshal's refusal to redeem the captives of a former raid. An auxiliary force came over from the marshal's Irish estates and was totally destroyed by Llywelyn. It was believed that the losses of the marshal and his men exceeded the amount of King Richard's ransom (Dunstaple Annals, p. 61; cf. Brut y Tywysogion, p. 307, and Royal Letters, i. 141-3, 145). Unable to defend themselves, the vassals of the earl were forced to make terms with the invader. The king, who indignantly repudiated all participation in Llywelyn's raid, urged in vain upon the prince to make reparation for the injuries that he had inflicted (Fœdera, i. 164). He was more successful in urging on Llywelyn to prolong the truce he had made with the Earl of Pembroke (ib. i. 166). Next year Llewelyn was occupied in a quarrel with his eldest son Gruffydd, born of a Welsh mother, who resented the favour shown to his legitimate half-brother Davydd, the grandson of King John. The men of Meirionydd, over which Gruffydd bore sway, grievously insulted Llywelyn, who now marched against them with an army. The intervention of 'the wise on both sides' prevented bloodshed. Gruffydd sulkily submitted to Llywelyn, who took away from him his dominions of Meirionydd and Ardudwy.
In the summer of 1221 Rhys the Hoarse of South Wales fell away from Llywelyn and attached himself to William Marshal. This again brought Llywelyn south of the Dovey. He took possession of Aberystwith and added it to his own domains (Brut y Tywysogion, p. 309), and afterwards fought against Rhys on Carmarthen bridge, where he gained the victory. He now stripped Rhys of Kidwelly, Gower, and his other southern possessions, and forced him to do homage and hand over hostages to him. Llywelyn then proceeded against Pembrokeshire, where this time he effected very little (Royal Letters, i. 176-7). In the autumn the restless prince had a fresh war on his hands. He attacked his old ally and son-in-law, Reginald de Braose, and laid siege to his castle of Builth. A royal army, accompanied by the young king in person, marched to its relief. The Welsh fled on its approach, and Henry marched as far as Montgomery, where he rebuilt or strengthened the castle (Matt. Paris, Hist. Major, iii. 64). In 1223 war raged more fiercely than ever in Pembrokeshire. In Passion week William Marshal came back from Ireland. Many magnates sent him help. He had now won back the castles that Llywelyn had captured, and retaliated by a destructive foray into Llywelyn's territories, where he won a pitched battle, slaying, it was believed, nine thousand men (ib. iii. 76).
The close understanding between Llywelyn and the discontented barons made the Welsh prince's activity the more dangerous. Hugh de Lacy was his active ally; Falkes de Breauté took refuge in his territory. The Earl of Chester was now his well-wisher, So formidable was he that after the failure
