Many centuries ago in the area where the river Dyfi meets the Atlantic Ocean, a great kingdom stood far out in the low lying land. The kingdom was called Cantref y Gwaelod and its many towns, farms and gleaming cities were protected from the sea by a series of sluices and dams.

The area was ruled over by a Prince called Gwyddno, who had ruled well for many years. In fact he had been so successful that the kingdom enjoyed a great period of prosperity, and the Prince and his subjects were want to overindulge in the more pleasurable aspects of life. As time went on the drinking, parties and wanton debauchery were the talk of the whole of Wales.

During this time the man in charge of upkeeping the solid defences against the sea was called Seithenyn. He was a Prince of Dyfed, and a man of high status in keeping with the importance of his task. At first he was diligent in all aspects of his role, but as time wore on he became addicted to the pleasures of the Court, in a state of drunken stupor most nights as well as much of the day, he began to neglect his duties. In time the dams became weather beaten and crumbling, and the sluices began to stiffen with rust. Many parts of the defences became leaky and with every pounding tide of the winter the dam became weaker.

One man began to notice the decay and the danger from the ever-encroaching sea. His name was Teithryn, and he was in charge of the Northern stretches of the dyke. While his vigilance in tending the Northern dams ensured they were sound his fears were ignored by courtiers, too busy with the night's entertainment to worry about the grumbling of a dam keeper.

Seithenyn also ignored his fears, he was by now a hopeless drunkard and in no fit state to be in charge of such a weighty responsibility.

One day in the depths of winter during the highest tides of the season, Teithynin, who was well versed in weather lore, saw the warning signs of a gigantic storm brewing. That night during the inevitable feasting, Teithryn drank very little and for the last time tried to warn the people of the approaching disaster. They laughed at him and told him to enjoy himself and stop worrying about something that could never happen

When he knew there was little time left, he went to the safety of high ground, and left the courtiers in their drunken stupor.

When the storm came it was the most furious in living memory, it brought before it a huge storm surge which swept over the dam as one great wave. Seithenyn cursing and shouting at the waves ran at the water with his drawn sword in an attempt to send back the waves, he was drowned instantly by a mighty weight of water.

The whole of the kingdom vanished beneath the waves that night, and out of the thousands of people only a few escaped. As well as Teithryn the vigilant Northern keeper, Gwyddno and a few of his subjects managed to drag themselves to shore where they lived in poverty for the rest of their lives lamenting their selfish ways.

Some of the ancient roadways and part of the dam system, is said to be still visible out in the bay during the lowest tides of the year.