BBC Radio Wales: Thursday May 25, 6.30pm; repeated Sunday May 28, noon & Wednesday May 31, 9.30pm.

If you're from Anglesey you'll probably know the story: in the sixth century two saints lived on the island - in the west there was Cybi, who lived in the old Roman fort at Holyhead, and in the east Seiriol who made his home by a well at Penmon. The two saints, so we're told, were good friends and would often walk 20 miles each to meet at Clorach near Llanerchymedd in the centre of Anglesey.

Both men would set off very early in the morning, Cybi heading east and Seiriol walking west. Meeting at Clorach they'd spend the day talking, arguing and praying together and, as the sun began to dip towards the western horizon, they'd take their leave of each other and to walk the 20 miles home again. Because Cybi had the sun in his face morning and evening he became known as Cybi Felyn ('the tawny') and his friend - who had his back to the sun - as Seiriol Wyn, the pale saint.

Radio Wales sent forth its own pair of saints - Frank Hennessy and Hywel Gwynfryn - to re-trace Cybi and Seiriol's footsteps. 'Cybi' Hennessy starts at Holyhead while Hywel 'Seiriol' Gwynfryn sets off from Penmon. Along the way they meet the priests of Holyhead and Penmon, local historians Eryl Rothwell Hughes, Ken Roberts, an artist who's been inspired by the story of Cybi and Seiriol ,and Eric Wyn Owen who dresses as Cybi for the annual procession through Holyhead on the saint's day. Hywel and Frank begin build up a picture of the two saints, the times in which they lived and the reason why they made their a round trip of 40 miles to meet each other.

Anglesey born and bred, Hywel has known the story of the two saints since childhood and vividly remembers learning the poem about the story at his school, Ysgol British in Llangefni. He was intrigued to visit some of Seiriol's haunts and says "As an Anglesey boy myself it's always a great pleasure to come back and visit the island."

The tale was new to Cardiffian Frank Hennessy, but by the time he reached Clorach he felt he knew Cybi extremely well. Says Frank: "I've seen the island from a completely different perspective, met some great people and learnt something about a truly extraordinary man - Cybi." And there was plenty of colour in Frank's cheeks at the end of the journey too, but it wasn't a suntan - just windburn from the biting Anglesey breeze.

A walk re-tracing the saints' footsteps is being organised for later this year by the churches in Holyhead and Beaumaris.