Beuno's activity was sponsored by Cadfan and other members of Gwynedd's Cuneddan dynasty; Aelhaiarn seems to have accompanied him out of Powys to Edeirnion and thence to northeastern Llŷn.

It claimed that Beuno (Byno) was accustomed to disappearing from his cell near Clynnog every night to travel 4 miles (6.4 km) to pray on a flat stone in the middle of the Afon Erch.

One night, as Beuno returned, he saw a man hidden in the dark; he then prayed that, if the stranger were on some good errand, he should attain it but, if his intent were ill, that some example be made of him.

(The latter, however, was long known as "Llanhaiarn" through a corruption of his name; the nearby estate known as Elernion ("St Elern's") is thought to have a similar origin.

[7] During expansion of the churchyard in 1865, workers discovered the Latin-inscribed gravestone of an Aliortus of Elmet, possibly indicating the existence of a religious settlement at the site before the arrival of Beuno and Aelhaearn.

[1] St Aelhaiarn's Well (Ffynnon Aelhaearn) at Llanaelhaearn was a major station on the northern pilgrimage route to Bardsey Island[14] and much frequented[8] for the miraculous cures associated with the "laughing" or "troubling of the water", an irregular appearance of upwelling bubbles throughout the well.

By the 19th century, the Llanaelhaearn well was surrounded with an oblong basin and stone benches; devotees would rest on them while waiting for the water to "laugh".

[16] During the Middle Ages, the inland reach of Meirionydd also bore a parish named Llanaelhaiarn near modern Gwyddelwern in Denbighshire.