Seiriol was a son of King
Owain Danwyn of
Rhos, and younger brother of
King Cynlas of
Rhos and
King Einion of
Llŷn. His cell at Penmon is said to have been rebuilt by his brothers, as they didn't think his humble residence was good enough. St Seiriol's
Well (Ffynnon Seiriol) lies in a small chamber adjoining its remains. Both are protected by
Cadw, the publicly funded body responsible for the historic monuments of Wales. Adjacent to them are the
church and ruins of a
monastery also dating back to Seiriol's day. According to legend, Seiriol and
Saint Cybi were good friends,
Rhyd-y-Saint railway station (
English: Ford of the Saints railway station) on the
Red Wharf Bay branch line near
Pentraeth was named so, since Seiriol and Cybi are said to have met there. St Seiriol's Well is a small rectangular pool set in a well chamber to the north of Penmon Priory church. In his old age, Seiriol retired to Ynys Lannog which subsequently became known (in
Welsh) as Ynys Seiriol. Later it would be known to the
Vikings as Prestholmr (Priestholm), and is known as
Puffin Island in
English since the 19th century. ==Veneration==