Cadwallon ap Madog was the son of Madog ab Idnerth who had died in 1140, while Idnerth was a grandson of Elystan Glodrydd who had died in around 1010 and had founded a dynasty in the Middle Marches of Wales, in the area known as Rhwng Gwy a Hafren (Between Wye & Severn).
After the death of Madog ab Idnerth, there was clearly a great deal of conflict in the Middle March between his family and the Norman Marcher lords.
The Brut y Twysogion records this with the words: And then the Lord Rhys ap Gruffudd prepared to go to the king’s court at Gloucester.
It seems he built Crug Eryr Castle and brought destruction to the English Marches of Herefordshire and Shropshire.
In this he appears to have been successful, but on returning home to Elfael he was met by men owing allegiance to Roger Mortimer of Wigmore and was cut down and killed on 22 September.