Llys Helig is the name of a natural rock formation off the coast at Penmaenmawr, north Wales.[1][2][3] There may be a fish weir to the south which tradition dates to the beginning of the 6th century. The sea level was low enough around 1600 AD to make the claims of Sir John Wynne of Gwydir feasible.[1][2][4] The earliest known use of the name Llys Helig for this rock formation is the Halliwell Manuscript which is believed to date to around the beginning of the 17th century, eleven centuries later.[2] Legends developed about it suggesting that it was the palace of Prince Helig ap Glanawg (also spelled Glannog) who lived in the 6th century, and whose sons established a number of churches in the area. He owned a large area of land between the Great Orme's Head near Llandudno and the Menai Strait off the north coast of Gwynedd.[citation needed]
This area was inundated by the sea, which gave rise to the legend of the drowned kingdom.[citation needed]
Llys Helig is mentioned in a number of old documents, some of which were published after expeditions to find the Palace. These include -
This last expedition reported finds of the remains of seaweed-covered walls, these walls indicating buildings some 100 yards long, and they concluded that this was indeed the palace.[citation needed]