The Battle of Mynydd Carn took place in 1081, as part of a dynastic struggle for control of the Welsh kingdoms of Gwynedd and Deheubarth.
The battle is recorded in the near-contemporary biography of one of the participants, The History of Gruffydd ap Cynan.
[2][3] In 1081, Gruffudd launched an invasion from Waterford in Ireland, having gathered a force of Danes and Irishmen to support his claim.
In the evening Gruffudd and Rhys came up with the forces led by Trahaearn and Caradog ap Gruffydd, who are reported to have had Norman arbalisters in their army.
According to his biography, Gruffudd ap Cynan insisted on an immediate attack, overruling Rhys who wished to wait until the following morning.