St. Constantine's son, Gereint rac Dehau or "Gerren for the South" was immortalised by Aneirin in his epic poem Y Gododdin. It tells of King Gerren's valiant death in 598, when the Celtic kingdoms under Kings Mynyddog Mwynfawr (the Wealthy) of Din-Eidyn (Edinburgh) & Cynan of Gododdin (Lothian) rode south to fight Saxon Bernicia against enormous odds at the Battle of Catreath (Catterick, Yorks).
However, it seems that Gerren may have only been mortally wounded at the battle, dying some days later. While fleeing to Brittany to escape plague in Wales, St. Teilo was entertained by King Gerren at his castle of Dingerein near the village of Gerrans on the Roseland Penninsula. He promised the King, he would not die without taking communion from the saint. Teilo did not return for seven years, when his ship was greeted by Dumnonian courtiers who emplored him to hasten to the dying King's side. Gerren was overjoyed to see his friend's return. He received the host and died in Teilo's arms. Far away, in Brittany, St. Turiau, saw his soul ascending to heaven.
His body, in full regalia, was placed in a great sarcophagus on a huge golden ship that slipped down "The Mermaid's Hole" and into the sea. He was then rowed across Gerrans Bay using solid silver oars and buried, ship and all, beneath the great barrow of Carne Beacon near Veryan. He waits, sword in hand, for the day when he will return to reclaim his Kingdom. Though excavated in 1855 no gold or silver, let alone a great ship, was found, only a small cist burial. Admittedly, the digging did only concentrate on the centre of the mound. The mermaid tunnel between the Dumnonian Royal Palace and the sea was said to have been rediscovered by a farmer in the 19th century. Gerren is revered as a saint at Gerrans parish church, at Magor in Gwent and at several sites in Brittany.