The ancient church is dedicated to St Tanwg, who may have founded it. Tanwg lived in the 5th century at a time when the Roman Empire in Western Europe was disintegrating. It may have been founded around 435CE as part of St Patrick’s communication system between Ireland and Britain.

We can safely say that St. Tanwg’s church is one of the oldest Christian foundations in Britain and perhaps the oldest with a continuous Christian history. The original church on this site was much smaller then the present building. It was probably built of stones carried from the beach, stone being the easiest and traditional building material in this locality, and roofed with oak timbers and thatch. The remains of this church may be under the present floor.
Because of its isolated position and the building of Harlech church, St Tanwg’s church escaped the improvements of the Victorian age and is of architectural interest for that, but its special value today is the light which it  is helping to shed on the last days of Roman Wales as Europe slid into the dark ages.
St Tanwgs, Llandanwg is a member of the Small Pilgrim Places Network