Nobody in Cantre'r GwaelodAn ancient kingdom that features in Welsh legends. The name means "district of the low land" in Welsh. had a greater responsibility than Seithennin. It was his job to oversee the sluicesSliding gates for controlling the flow of water. that protected the low-lying kingdom, opening them at low tide to drain the land and closing them in time to stop the sea flooding it. But one night he got drunk and went to bed leaving the gates open. At high tide, the kingdom disappeared forever beneath the waves.

According to Welsh legend, Cantre'r Gwaelod was situated on land which is now under Cardigan Bay. It was a wealthy kingdom containing 16 splendid cities, with a large population. Its story is told in the Black Book of Carmarthen, the earliest written collection¹ of Welsh poetry, while Giraldus CambrensisA medieval historian. "Cambrensis" is Latin for "Welsh". wrote about a drowned forest there called Newgale.

In more recent times, people have claimed to see the outlines of buildings beneath the waves, and heard bells ringing from under the sea. Remains of ancient forests are sometimes exposed by stormy weather.  

The story has generally been dismissed as a myth like that of AtlantisAn island or city said to have disappeared beneath the see. The legend goes back to Ancient Greek times. . But now an expert on geography, Simon Haslett, and an expert on Celtic literature, David Willis, believe they have found evidence that it is rooted in fact.

They argue that Cantre'r Gwaelod is one of two islands that used to exist off the coast of Wales. They are shown on the earliest surviving complete map of the British Isles, the Gough MapThe earliest surviving complete map of the British Isles. It is drawn on two pieces of animal hide which together measure approximately two by four feet., which dates from the 13^th or 14^th Century.   

"The Gough Map is extraordinarily accurate considering the surveying tools they would have had at their disposal at that time," says Haslett. "The two islands are clearly marked and may corroborateSupport a statement or theory. It comes from a Latin verb meaning to strengthen. contemporary accounts of a lost land."

He adds that according to PtolemyAn early mapmaker. He lived in Egypt in the 2nd Century AD, when it was a Roman province., the early cartographerMapmaker., the Welsh coastline may have been eight miles further west than it is now. Haslett suggests that the flooding legend might refer to people being forced to move inland by erosion or a dramatic event like a tsunami.

Archaeologists have made extraordinary discoveries about lost civilisations. In 1986 they uncovered pits full of gold and bronze treasures in the Sichuan province of China. They had belonged to the Sanxingdui people, who flourished in the 12th Century BC.

Between 6,000 BC and 3,000 BC, the Trypillia culture dominated what is now Moldova and parts of Ukraine and Romania. Surviving pottery shows highly sophisticated designs. But every 60 to 80 years they would burn their settlements to the ground and start again.

One of the most spectacular discoveries in the Middle East was Petra, the capital of the Nabatean people. It includes beautiful buildings carved out of the rockface. But between the 13th and 19th Centuries no one knew where to find it.

In Orkney, the Neolithic settlement of Skara Brae lay buried under the sand for millennia until a storm suddenly revealed it in 1850. It showed evidence of a surprisingly complex society.

Today some commentators worry that our own society could collapse and disappear in a similar way.

Yes: The world is in a state of chaos, brought about by war, the pandemic, economic recession, feeble governments and dishonest politicians. Our civilisation is no better than those that came before, and could easily be forgotten.

No: The human race is making enormous advances all the time, and AI will make them even more spectacular. The society of Cantre'r Gwaelod would look pitiful by comparison. 

Or... Civilisation is about how people think and behave, not the technology available to them. People from past centuries would think we have ridiculously easy lives and lack their resourcefulness.