In 1114 a new war between Gruffydd and the Earl of Chester led to an invasion of Gwynedd by Henry I in person. After Owain ab Cadwgan had been tricked into making peace, Gruffydd also sought peace and was pardoned in return for a large tribute (Brut y Tywysogion, sub an. 1111; Ann. Cambr. sub an. 1114). In 1115 Gruffydd ab Rhys (d. 1136) [q. v.] of South Wales took refuge with Gruffydd ab Cynan. According to the 'Brut y Tywysogion,' Henry I sent for the northern Gruffydd and persuaded him to give up his fugitive namesake. When Gruffydd ab Rhys took sanctuary at Aberdaron, Gruffydd ab Cynan was only prevented by the remonstrances of the clergy from violating the sanctuary. Gruffydd ab Cynan remained for several years at peace with Henry. In 1120 he ended the long vacancy of the see of Bangor by procuring the election of Bishop David (d. 1139?) [q. v.], and wrote a letter to Archbishop Ralph which procured the consecration of his nominee (Eadmer, Hist. Nov. p. 259, gives the letter). In 1121 he supported Henry when that king invaded Powys, and entirely deserted the sons and grandsons of Cadwgan (Brut y Tywysogion, sub an. 1118). During his old age he put his sons over the remoter cantreds of his dominions, and they ravaged Powys and Ceredigion in many a bloody foray. Towards the end of his life Gruffydd became again on good terms with Gruffydd ab Rhys.
The latter part of Gruffydd's reign is celebrated as a period of peace and prosperity by his biographer. Between 1130 and 1135 were 'four successive years without any story to be found' (ib.), so quiet were the times. Gruffydd was especially praised 'for collecting together into Gwynedd those who had been before scattered into various countries by the Normans.' He thus made Mon and Gwynedd the centres of the national life.
His fame rose above that of the other petty Welsh rulers, and Ordericus (Hist.Eccl. iv. 493) couples him as 'princeps Brittonum' with Henry I himself the 'princepsAnglorum.' He prepared the way for the great resistance to Norman aggression which, under his son Owain, preserved the independence of Gwynedd. He was a good friend to the clergy, and built so many churches that, says his biographer, 'Gwynedd became splendid with white churches like the firmament with stars.' In his will he left donations to many Welsh, Irish, and English churches. Gruffydd's reign marks an epoch in the growth of Welsh literature. He gave the same impulse to the poets of the north that Rhys ab Tewdwr's return from Brittany and the curiosity of the Norman conquerors gave to the prose writers of South Wales. Meiler, the oldest of the Welsh bards, who had lamented in his youth the fall of Trahaiarn at the hands of Gruffydd, wrote in his extreme old age an elegy on Gruffydd himself, which is almost the first Welsh poem of literary value whose date can be precisely fixed. A long series of bards, of whom Gwalchmai, Meiler's son, was one of the most distinguished, now flourished in North Wales. The loss of Gruffydd's pencerdd (chief bard) at the fight at Aberlleiniog (Life, p. 118) was worthy of special mention by his biographer.
Dr. Powel in his 'History of Cambria,' 1584, says that Gruffydd 'reformed the disordered behaviour of the Welsh minstrels by a very good statute which is extant to this day.' In 1592 Dr. John David Rhys published these laws in his 'Cambro-Brytannicæ Linguæ Institutiones.' They were said to have been promulgated at a great gathering of bards and minstrels at Caerwys, though the Earl of Chester rather than Gruffydd must always have borne rule in the region that is now Flintshire. There is no reference to such an assembly in the best manuscript of the biography of Gruffydd, but in a manuscript of inferior authenticity, 'The Book of Richard Davies of Bangor,' is a passage describing the Caerwys meeting, and telling how the chief prize at the Eisteddfod was gained by a 'Scot' (Irishman), who was presented by Gruffydd with a golden pipe (Myvyrian Archæology, ii. 604, note, translated in Stephens, Literature of the Kymry, p. 57). Gruffydd's Irish education is thought to have led him to introduce bagpipes into Wales, somewhat to the disparagement of the harp. His musical laws are also said to have been largely derived from Irish sources. It has been debated with much animation among Welsh antiquaries, whether these Irish innovations in any way impaired the originality of the national music (T. Price (Carnhuanawc) Hanes Cymru; but cf. the more moderate comments of Stephens, Literature of the Kymry, p. 58). The 'Gwentian Brut'; (p. 112) says that Gruffydd was present at a great South Welsh gathering of minstrels held by Gruffydd ab Rhys in 1135.
In his old age Gruffydd is said to have become blind. He died in 1137 (Annales Cambria), having assumed the monastic habit and having received extreme unction from Bishop David of Bangor. He was eighty-two years old. He was buried in a splendid tomb at Bangor on the left of the high altar (Life).
Gruffydd is described by his biographer as of low stature, with yellow hair, a round face, fine colour, large eyes and very beautiful
