It is about a quarter of a mile (400 m) from the Menai Strait, which divides the mainland of Wales from the island of Anglesey.[4] The authors of a 2009 guide to the buildings of north-west Wales record the tradition that a church was first established at this site in 616.[5] St Nidan, who founded the church, was associated with St Seiriol's monastery at Penmon, on the eastern tip of Anglesey, and was the monastery's confessor.[6] The area takes its name from the church: the Welsh word llan originally meant "enclosure" and then "church", and "‑idan" is a modified form of the saint's name.[7]