Sunken realms – the lost lands of Wales

Sarn Gynfelyn at low tide (photo by Dave Croker,

There are legends of flooded lands around the coast of Britain, and no more so than in Wales. These lands were inundated by the sea, through gradual sea level rise or during catastrophic events. This article focuses on submerged lands off the west and north-west coasts of Wales. How, and when, did they succumb to the seas?

The most well-known of Britain’s lost lands is probably Lyonesse, said to lie off the coast of Cornwall. Like the lost city of Kêr-Is over in Brittany, there are legends of its sudden inundation by the sea. There are also legends that – years later – the bells of drowned churches can still be heard ringing (a common tale when it comes to sunken settlements).

One part of Britain that has more legends of lost lands than most is the country of Wales….

“Cornwall and Lyonnese are fascinating, but Wales probably has more lost lands and legends than the rest of England put together” – Lionel Fanthorpe

“The principality of Wales has lost more territory to the sea than other parts of Britain, and owing to its long unbroken culture, we have documentary evidence of the inundated lands” – Nigel Pennick

“All along the coast of Wales are submerged forests, submerged walls, ancient roads apparently going into the ocean and other indications of a sunken land. These inundations probably have taken place in the last few thousand years, during the time of recent folk memory” – David Hatcher Childress

Off the coast of St David’s

The lost Realm of Teithi Hen is referred to in the 13th century Chronica de Wallia. Its ruler was Teithi Hen, or ‘Teithi the Old’. The story tells of how Teithi alone survived the flooding of his land. He fled on horseback, and it is said that “afterwards for all the days of his life he was weak with fear”. Such an escape by horseback is also seen in the legends of Lyonesse and Kêr-Is.

In this case, it is associated with a land described as being between Mynwy (taken to mean St David’s) and Ireland. The St George’s sea channel, which today divides Wales and Ireland, was dry land during the Ice Age. When the Ice Age ended, sea levels rose and the land was flooded.

There have however been more recent inundations in Cardigan Bay to the north. The river valley leading down to Cardigan is called Teifi (very similar to Teithi, as it happens). And it is in Cardigan Bay that we find compelling stories – and evidence – of flooded lands.

Cardigan Bay

The lost “Lowland Hundred” of Cantre’r Gwaelod is said to be located in what is now Cardigan Bay. It has been dubbed the “Welsh Atlantis”. The ‘Hundred’ or ‘Cantref’ refers to a medieval Welsh land division. ‘Gwaelod’ refers to Gwyddno Garanhir, the person who is usually depicted as ruler of this land.

According to the most popular version of the legend, there were 16 fortified towns in Cantre’r Gwaelod, the principal of which was Caer Wyddno, the city of Gwyddno Garanhir himself. Gwyddno oversaw the construction and maintenance of a sea wall around the coast of his land. One night, one of the gate-masters, called Seithenyn, drunk himself into a stupor and failed to close the flood-gate. The sea poured in, and at least one thousand people are said to have drowned.

An earlier version of the story, in the Black Book of Carmarthen, refers to the lost land as “Maes Gwyddno” (the Plain of Gwyddno). It attributes the flooding of the land to a well-maiden called Mererid, who allowed a well to overflow.

There are various references to the extent of the former lands in Cardigan Bay, some suggesting that they ran from Cardigan in the south to the Lleyn peninsula in the north. A smaller area is also talked about, extending some 20 miles out from the current coastline, with its northern extent defined by Sarn Badrig, also known as St Patrick’s Causeway.

Sarn Badrig is one of several roughly parallel causeways (or sarnau) extending out from the coast in Cardigan Bay. Another of these causeways was called Sarn Gynfelyn (see photo at top), at the end of which Caer Wyddno, or Gwyddno’s Fortress, was apparently located. In the past, these causeways were considered to be ancient roads extending into the lost land of Cantre’r Gwaelod. Geologists now consider them to be natural shingle reefs, made up of glacial deposits left by receding ice sheets.

Map of Cardigan bay showing some of the causeways or sarnau

UPDATE August 2022: News about two islands in Cardigan Bay shown in medieval map...

Map may show evidence of Wales’ Atlantis off Ceredigion – BBC News

Digital map. Gough Map.

Caernarfon Bay

The legendary lost palace of Caer Arianrhod was thought to lie beneath the waters in Caernarfon Bay. ‘Caer’ means fortress or citadel in Welsh, and Caernarfon refers to the nearby town of the same name. Arianrhod – on the other hand – was a female figure in Welsh mythology, who played her most important role in the fourth branch of the Mabinogi.

On modern maps of Caernarfon Bay, there is an oval formation called Caer Arianrhod around 1km offshore, which is said to become visible at low tide. There is also a submerged area of stony ground that connects it to the coast. In a map drawn up in 1568, this oval formation was labeled as ‘Caer Lerjenrhod’. A few centuries later, antiquarians alleged to have seen a long line of walls and buildings, and found stones incised with six-armed crosses.

Late 19th century map showing Caer Arianrhod

Today, the consensus is that the oval rock formation is a natural feature, and that underwater structures nearer the coastline are associated with coastal fishing industries. Disappointingly, there seems to be a lack of more compelling evidence linking the submerged rocks with Arianrhod of Welsh mythology.

Conwy Bay

The lost land of Tyno Helig (or Helig’s Vale) is said to lie under the sea in Conwy Bay, off the north coast of Wales. The bay is bounded by the Isle of Anglesey in the west, and the imposing Great Orme headland in the east. The River Conwy enters the bay adjacent to the Great Orme.

A tranquil sea in Conwy Bay from Gogarth, Great Orme (photo by Bill Boaden from

According to legend, this lost land was ruled by Helig ap Glannawg. Helig lived in Llys Helig (Helig`s Court or Palace), set within a fertile valley. As the story goes, one night a great feast was held at Llys Helig. A maid went into a cellar to fetch some more wine and saw that it was half filled with sea water. She fled with her lover, the court jester, and the next day Llys Helig had vanished under the sea.

In another version of the story, Helig and his numerous sons are said to have been the sole survivors of the inundation. They took shelter on the hill above Penmaenmawr, which now overlooks the bay. Their survival meant they had the opportunity to repent their vices and lead moral lives. They apparently went on to establish a number of churches.

In terms of Llys Helig, author Marc Alexander reports that it was a long-held belief among local residents that at low tide its ruins were visible from fishing boats. On some old maps, a rocky reef not far offshore was labeled as Llys Helig. However, Paul Dunbavin concludes that “there is no doubt that the rocks of Llys Helig are entirely natural and the immediate source of the legend can be traced back no further than a few paragraphs in a local survey, written about the year 1620”.

Map of Conwy Bay from 1841 with annotation added
The meaning of Helig

The lost land of Tyno Helig may have been named after Helig ap Glanawg, yet the word Helig has similarities with islands off the North Sea coast. Halligen (German) or hallinger (Danish, singular hallig) are small islands without protective dykes (banks of earth), or land lying seaward of a dyke. According to the Wikipedia page for Halligen

“The name is cognate to Old-English halh, meaning “slightly raised ground isolated by marsh”. The very existence of the Halligen is a result of frequent floods and poor coastal protection. The floods were much more common in the Middle Ages and coastal protection was much poorer. A look at the maps on this page will demonstrate that this part of the North Sea coast is very much at the sea’s mercy”

Perhaps the same could be said of low-lying coastal areas of Britain – that during the Middle Ages they were inundated by the seas due to frequent floods and poor coastal protection. So does this mean that the legendary lost lands of Wales were submerged in the Middle Ages? (i.e. 5th to 15th century)

Dating the inundations

The challenge to establish accurate chronologies based on legends has its pitfalls. In the word’s of Paul Dunbavin… “In Welsh legend, names and characters survive well, sequence and consistency do not!”

The scholar Rachel Bromwich concluded that the legends associated with Cardigan Bay and Conwy Bay could have influenced each other: “The widespread parallels to this inundation theme would suggest that the two stories are in fact one in origin, and were localized separately in Cardiganshire and in the Conway estuary, around two traditional figures of the sixth century”.

There are however counter arguments to the suggestion that the inundations took place in the sixth century. Paul Dunbavin points out that historical sources (namely Gildas and Nennius) did not mention any lost lands or serious flood catastrophes in the sixth century. He suggests the Welsh shoreline may not have altered since Roman times.

One exception to this appears to be Lavan Sands, on the west side of Conwy Bay. They lie between the Welsh mainland and the town of Beaumaris (“beautiful marshes”). Lavan Sands are exposed at low land, and there is evidence that they were once crossed by causeways. An early 19th century source indicated that when the tide was at very low ebb, ruined houses could be seen, and a causeway from Penmaenmawr across to Preistholm (now Puffin Island).

Lavan Sands is fabled to have once been a flourishing plain, thickly inhabited, and suddenly submerged. The name Lavan Sands is thought to derive from the Welsh word “to weep”, supposedly reflecting the response of locals to the terrible loss of the land and its inhabitants. Nigel Pennick concludes that a great inundation led to the submergence of Lavan Sands sometime between the years AD 634 and 664.

A late 18th century map of Conwy Bay showing a causeway across Lavan Sands
The view over Lavan Sands today (photo by Ian S. from

Turning to Cardigan Bay, the lost lands may have been inundated at a much earlier time. The remains of a submerged forest have been found in the beaches at Borth and Ynyslas, just north of Aberystwyth. These indicate that the lost lands in Cardigan Bay were forested and probably inhabited 7,000 years ago (i.e. 5000 BC). Gradual sea level rise may have submerged these lands. Alternatively, Paul Dunbavin favours their sudden drowning at two periods: around 3100 BC and possibly again around 1600 BC.

Remains of submerged forest in the beach at Borth

No doubt further research – including dating of the submerged forest and mapping of the sea bed – will help to refine these dates and improve our understanding. For now, it is easy to relate to the conclusion of Edward W. Cox, a nineteenth century antiquarian writing on the submerged lands of Wales…

“Thus, from age to age, the forces that make and unmake our world go on…”



Alexander, Mark – A Companion of the British Folklore, Myths and Legends, Sutton Publishing, 2002

Childress, David Hatcher – Lost Cities of Atlantis, Ancient Europe and the Mediterranean, Adventures Unlimited Press, 1996

Dunbavin, Paul – The Atlantis Researches, Third Millennium Publishing, 1995 [updated and re-published as Atlantis of the West, 2002]

Pennick, Nigel – Lost Cities and Sunken Lands, Capall Bann Publishing, second edition, 1997

Senior, Michael – Llys Helig and the myth of the lost lands, Gwasg Carreg Gwalch, 2002

Westwood, Jennifer – Albion – A Guide to Legendary Britain, Paladin, 1987

Other sources

BBC article: Cantre’r Gwaelod – The Lost Land of Wales

BBC article: Experts look for ‘watery kingdom’

Coflein webpage on Caer Arianrhod reef, Llandwrog

Coflein webpage for Submerged Forest, Borth Sands

Lost worlds – The sunken realm of Tyno Helig, article by zteve t evans

Traces of submerged lands on the coasts of Lancashire, Cheshire and North Wales, by Edward W.Cox, 1893 [PDF]

Tyno Helig – the Welsh Atlantis?, article by Ben Johnson

Wikipedia – including the pages on Arianrhod, Cantre’r Gwaelod, Halligen, Helig ap Glanawg, Llys Helig and Sarn Badrig

Be the first to comment

Leave a Reply

Your email address will not be published.


This site uses Akismet to reduce spam. Learn how your comment data is processed.