Cadwallon was the son of Einion Yrth ap Cunedda and Prawst ferch Deithlyn.
[3] According to one tradition, Cadwallon and his army padlocked their own feet to their stirrups so that they could not be tempted to flee the battle.
[4] Cadwallon's opponent, the leader of the Irish of Angelsey, was said to be Serigi Wyddel (Serigi "The Irishman"), and the final battle was fought at either Cerrig y Gwyddyl or Llan y Gwyddyl near Holyhead.
This was indicated on the Ordnance Survey map of 1889 as within a field near Mynydd Eilian, in the Llaneilian community, in the north-east corner of the Isle of Anglesey.
With no obvious remains by the 20th century, it had been largely discredited as a Llys site until a geophysical survey in 2009 identified foundations of a rectangular building within a trapezoidal enclosure, for which an early medieval site was a strong possibility.