Prince Ceidio of Gwent became embroiled in political intrigue while still a baby, for he escaped with his mother, Queen (& Saint) Madrun of Gwent, from the flames of High-King Vortigern's last stand at Tre'r Ceiri. He settled at Llangeidio just north of his mother's hillfort on Carn Fadrun, and founded a church there. Like many Celtic saints, upon taking up the religious life, he may have become associated with a sanctuary-seeking deer, for his horse was called one of the three "cloven-hoofed horses" of Britain. He founded other churches in Wales at Ceidio (Llandyrnog) and Rhaeadr (Gwerthrinion), but later took his mother to Cerniw to evangelize the people of Minster. He is sometimes, mistakenly, recorded as Cynheiddon and should not be confused with St. Ceidio ap Caw.