He was defeated and killed here by the forces of his half-brothers Dafydd ab Owain Gwynedd and Rhodri.
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In 1170 it was the site of a battle when Hywel ab Owain Gwynedd landed with an army raised in Ireland in an attempt to claim a share of the kingdom of Gwynedd following the death of his father Owain Gwynedd.
Rhyd-y-Saint railway station (English: Saints' Ford) on the Red Wharf Bay branch line near Pentraeth, was named so as Cybi and Seiriol are said to have met there.