Dominance of Gwynedd and Edwardian conquest: 1216–1283 thumb|right|The Llywelyn Monument at Cilmeri Out of the power struggle in Gwynedd eventually arose one of the greatest of Welsh leaders, 's grandson, Llywelyn ab Iorwerth, also known as Llywelyn Fawr (the Great). Llywelyn ab Iorwerth was sole ruler of Gwynedd by 1200 and by his death in 1240 was effectively ruler of much of Wales. Llywelyn made his 'capital' and headquarters at Abergwyngregyn on the north coast, overlooking the Menai Strait. In 1200 he became King of Gwynedd and agreed to a treaty of peace with King John of England, marrying his illegitimate daughter Joan. In 1208, Llywelyn claimed the Kingdom of Powys after the arrest of Gwenwynwyn ap Owain by King John, who disapproved of his attacks on Marcher Lords of the South. Friendship broke down and John invaded parts of Gwynedd in 1211, taking Llywelyn's eldest son as hostage, and also forcing the surrender of territory in north-east Wales. Llywelyn's son, Gruffydd ap Llywelyn, and other hostages were used as security by the king. However the Welsh and Scots joined English rebel Barons in forcing John to sign the Magna Carta of 1215. The document therefore holds specific Welsh provisions. These included the return of lands and liberties to Welshmen if those lands and liberties had been taken by English (and vice versa) without a law abiding judgement of their peers. Also the immediate return of Gruffydd and the other Welsh hostages. Llywelyn went on to gain dominance over all Wales the following year.
Dominance of Gwynedd and Edwardian conquest 1216–1283 thumb|right|The Llywelyn Monument at Cilmeri Out of the power struggle in Gwynedd eventually arose one of the greatest of Welsh leaders 's grandson Llywelyn ab Iorwerth also known as Llywelyn Fawr (the Great) Llywelyn ab Iorwerth was sole ruler of Gwynedd by 1200 and by his death in 1240 was effectively ruler of much of Wales Llywelyn made his 'capital' and headquarters at Abergwyngregyn on the north coast overlooking the Menai Strait In 1200 he became King of Gwynedd and agreed to a treaty of peace with King John of England marrying his illegitimate daughter Joan In 1208 Llywelyn claimed the Kingdom of Powys after the arrest of Gwenwynwyn ap Owain by King John who disapproved of his attacks on Marcher Lords of the South Friendship broke down and John invaded parts of Gwynedd in 1211 taking Llywelyn's eldest son as hostage and also forcing the surrender of territory in north-east Wales Llywelyn's son Gruffydd ap Llywelyn and other hostages were used as security by the king However the Welsh and Scots joined English rebel Barons in forcing John to sign the Magna Carta of 1215 The document therefore holds specific Welsh provisions These included the return of lands and liberties to Welshmen if those lands and liberties had been taken by English (and vice versa) without a law abiding judgement of their peers Also the immediate return of Gruffydd and the other Welsh hostages Llywelyn went on to gain dominance over all Wales the following year