Located on Church Island, in the shadows of the Menai Strait bridges, St. Tysilio's is one of the most familiar of the small churches on the island. The churchyard and the nearby Belgian Promenade are popular promenade routes for local residents and tourists alike.

Tysilio was the son of Brochfael Ysgythrog, king of Powys. He fled his father's court to follow the religious life, eventually coming to Anglesey where he founded a hermitage on an island in the Menai Strait around 630AD. After seven years he moved on to become Abbot at Meifod, Powys, where he had started his religious training. He is thought by many to be the same person as St. Suliac, who set up a religious centre in Brittany.

Source: https://www.anglesey-history.co.uk/places/churches_and_chapels/Llandysilio/index.html