Warrior made captive

On 3 April 1263 Dafydd ap Gruffudd met Lord Edward at Hereford and offered his allegiance to the English prince. Under the terms of their agreement, Dafydd was promised the cantref of Dyffryn Clwyd and the commote of Rheinmerch in Rhufoniog until he recovered his full inheritance in Gwynedd Uwch Conwy. In a further agreement, ratified by Henry III at Windsor on 8 July, this was replaced by the grant of Dyffryn Clwyd and the whole of Rhufoniog.

The agreement at Hereford was struck when Edward was about to set out on campaign against Dafydd's brother, Prince Llywelyn. Dafydd's motives for deserting his brother, at such a time, are complicated. They had a troubled relationship. As a youth, Dafydd had been deprived of much of his share of Gwynedd, when Llywelyn and another sibling. Owain Goch, divided much of the land between themselves. This triggered a civil war, in which Llywelyn emerged the victor. Owain was imprisoned, but Dafydd given a chance to redeem himself. 

He remained loyal to Llywelyn for eight years, until the spring of 1263, and the decision to join with Edward. It is likely that Dafydd was still unhappy with the division of land in Gwynedd, even though Llywelyn had permitted him to rule Dyffryn Clwyd. Ultimately, Dafydd would not be satisfied with anything less than an equal share.

According to the Annals of Chester, Dafydd was also anxious to secure the release of his brother, Owain Goch, from prison at Dolbadarn castle. This was certainly a bone of contention inside Gwynedd. A Venedotian poet, Hywel Foel ap Griffri, described Owain as 'a warrior made captive by the lord of Eryri'.

Llywelyn ignored any such calls for Owain's release. In his eyes, the prisoner was too dangerous, and threatened Llywelyn's hegemony. There was also the looming threat of the king of England, who regarded Owain as the rightful heir to Gwynedd. At the same time Llywelyn was not bloodthirsty, and refused to simply kill his rebellious brothers.

The Hereford treaty of 3 April marked the start of a 19-year alliance between Dafydd and Edward. They worked together to destroy Edward's enemies in England and Wales, until Dafydd's career took another shocking turn.