GWENWYNWYN (d. 1218?), prince of Powys, was the eldest son of Owain Cyveiliog, prince of Powys. In 1186 he is first mentioned as joining with his brother Cadwallon in slaying Owain, son of Madog, by treachery (Brut y Tywysogion, s.a. 1186). In 1196 he was engaged in war with Archbishop Hubert Walter and an army of English and North Welsh. His castle of Trallong Llewelyn (Pool Castle, Eyton, Shropshire, x. 358) was besieged and taken by undermining the walls; but the garrison escaped, and before the end of the year Gwenwynwyn again took the castle (Brut y Tywysogion, p. 245). In 1197, after the death of the Lord Rhys of South Wales, Gwenwynwyn took part in the struggle of Maelgwn and Gruffydd [see Gruffydd ab Rhys, d. 1201] the sons of Rhys, and actively supported Gruffydd. When Maelgwn took Gruffydd prisoner he handed him over to Gwenwynwyn's custody. But Gwenwynwyn transferred his care to the English. Gwenwynwyn next subdued Arwystli and captured Llewelyn ab Iorwerth, then just beginning his great career. It is hard to believe, however, that he took Davydd ab Owain [see Davydd I, d. 1203] prisoner as well, though some manuscripts of the 'Brut' say so.
The death of Owain Cyveiliog in 1197 made Gwenwynwyn prince of Powys. As his father had previously taken the monastic habit at Ystrad Marchell (Strata Marcella), it is likely that he had already practically ruled the district. He now formed great plans for restoring to the Welsh their ancient rights, property, and boundaries; assembled a great army in July, and besieged William de Braose in Maud's Castle (ib. p. 253; Hoveden, iv. 53, ed. Stubbs). The siege was relieved by the justiciar Geoffry Fitzpeter, who put the Welsh to flight and slew 3,700 with the loss of only one man. King John, however, made friends with him again, and made him grants of land.
In 1202 Gwenwynwyn was fiercely attacked by Llewelyn ab Iorwerth, now lord of Gwynedd, who, says the 'Brut,' 'though near to him in kindred was a foe to him as to deeds,' but the clerks and monks patched up a peace between them. In the next year Gwenwynwyn was much occupied in helping Maelgwn in his war against his brother, Gruffydd ab Rhys [q. v.] In 1203 William de Braose again complained that Gwenwynwyn was destroying his lands (Rot. Lit. Pat. i. 23). Next year Gwenwynwyn received a safe-conduct to meet the king at Woodstock, and the result of the interview apparently proving satisfactory, he received back the lands at Ashford in Derbyshire granted to him by John in 1200 (Rot. Lit. Claus. i. 24 ; Rot. Chartarum, p. 44). He soon quarrelled again with the king, who in 1207 enticed him to Shrewsbury and threw him into prison, Llewelyn ab Iorwerth seizing on all his lands. Next year Gwenwynwyn made a composition with John, took oaths of fealty, and handed over twenty hostages for his fidelity (Fœdera, i. 101). He was restored to his territories, received various gifts from the crown (Rot. Misæ, 111, 141, 154), and in 1210 followed John on his expedition against Llewelyn, but next year he joined Llewelyn in a new revolt from John. Innocent III absolved them and the other Welsh princes from their allegiance to the excommunicated king, and they all levied war against him. In 1215 Gwenwynwyn accompanied Llewelyn in his victorious expedition to the south. King John now deprived him of Ashford, which he granted to Brian de L'Isle (Rot. Lit. Claus. i. 185b). In 1216, however, Gwenwynwyn made peace with King John, to the great indignation of Llewelyn, who speedily overran his dominions, took possession of them all, and drove Gwenwynwyn to take refuge in Cheshire. John restored his lands, and thanked him for his help (Rot. Lit. Pat. i. 175, 189; Rot. Lit. Claus. i. 246b), but he never regained his possessions. On his death, apparently in 1218, Llewelyn agreed to provide a sufficient sum for their revenues to maintain his family, and to give his widow her reasonable dower, but bargained to hold them until his sons came of age (Fœdera, i. 151). Brian de L'Isle was also required to give to the widow her dower from his lands at Holme and Ashford (Rot. Lit. Claus. i. 536b). Gruffydd's wife was Margaret, daughter of Robert Corbet (Eyton, Shropshire, vii. 22-3). Their eldest son was Gruffydd [see Gruffydd ab Gwenwynwyn]. Gwenwynwyn had other sons named Owain and Madog (Montgomeryshire Collections, i. 21). In the days of his prosperity Gwenwynwyn had been a liberal benefactor to the Cistercians of Ystrad Marchell, or Strata Marcella (ib. v. 114-19). From him the district of Upper Powys, over which he had ruled, became known as Powys Gwenwynwyn.[Brut y Tywysogion (Rolls Ser.); Rotuli Litterarum Clausarum et Patentium, Record Comm.; Fœdera, vol. i., Record ed.; Eyton's Shropshire; Bridgeman's Princes of Upper Powys, in the Montgomeryshire Collections of the Powysland Club, i. 11-19, 104-11.]