Saint Tysilio (+640 AD) was a Welsh bishop, prince and scholar, son of the reigning King of Powys, Brochwel Ysgithrog, maternal nephew of the great Abbot Dunod of Bangor Iscoed, and an ecclesiastic who took a prominent part in the affairs of Wales during the distressful period at the opening of the 7th century
Prince Tysilio (or Sulio) was the second son of Brochfael Ysgythrog (of the Tusks). He fled his father’s court at an early age to throw himself on the mercy of Abbot Gwyddfarch of Caer-Meguaidd (Meifod) and beg to become a monk. A Powysian warband was sent to retrieve him, but King Brochfael was eventually persuaded that his son should be allowed to stay. Tysilio probably started his career in Trallwng Llywelyn (Welshpool) and afterward took up residence in Meifod where he was associated with Gwyddvarch and St Beuno.
Fearful of further trouble from his family, Tysilio set up his base at a hermitage on Ynys Tysilio (Church Island) in the Menai Straits and became a great evangelizer on Ynys Mon (Anglesey). He spent seven years there before returning to Caer-Meguaidd (Meifod) and succeeding as Abbot. Tyslio rebuilt the Abbey Church and things were peaceful for a while. He founded the second church in Meifod – the Eglwys Tysilio. His feast day, or gwyl-mabsant, was 8 November which was also the date of the patronal festival and “wakes” in the nearby parish of Guilsfield, where a holy well was dedicated to him – the Fons Tysilio.
After the death of Tysilio’s brother, his sister-in-law, Queen Gwenwynwyn, desired to marry Tysilio and place him on the throne of Powys. Objecting to both proposals, Tysilio refused and found his monastery persecuted by the state. He resolved to leave for Brittany with a handful of followers. Tysilio traveled through Dyfed and across the Channel to Saint-Suliac where he established a second monastery.