Cadwallon Lawhir ap Einion

Cadwallon ap Einion (c. 460-517 or 534), usually known as Cadwallon Lawhir ('Long Hand') and also called Cadwallon I by some historians, was a king of Gwynedd. He was said to have been a son of Einion Yrth and Prawst ferch Deithlyn. 
Cadwallon's reign is believed to have run from his father's death in about 500 until his own death some time between 517 and 534. He is often credited with having driven the last Irish settlers off the island of Anglesey. 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.
Cadwallon's epithet, "Lawhir", may possibly refer to him having longer than usual arms or might also be a metaphor, referring to the extent of his authority. The late medieval poet Iolo Goch claims that he could "reach a stone from the ground to kill a raven, without bending his back, because his arm was as long as his side to the ground."
According to Gildas, Cadwallon's son, Maelgwn Gwynedd, murdered his uncle in order to ascend the throne, which suggests that someone other than Maelgwn himself inherited the kingdom upon Cadwallon's death. No clear evidence exists as to who this "lost king" might be (assuming, of course, that Gildas's account is reliable), but some have suggested the name of Owain Ddantgwyn as the unfortunate predecessor.
Caswallon's Llys.
There has been a longstanding association, in antiquarian writings, between Cadwallon and a possible Llys (medieval royal court building) known as Caswallon's Llys. This was indicated on the Ordnance Survey map of 1889 as within a field near Mynnydd 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.