Ever heard of the Kingdom of Cantre'r Gwaelod?
If not, I hadn't either. Those of you with a linguistic bent might surmise from the name that the kingdom had something to do with Wales, and you'd be right. The sad tale of the lost Kingdom of Cantre'r Gwaelod is one of the dozens of inundation myths (although using that last word may be inappropriate, as you'll see in a moment), including the Breton city of Ys and the Arthurian legend of the Kingdom of Lyonesse. Both were allegedly destroyed for their wickedness by drowning in the ocean. If this puts you in mind of J. R. R. Tolkien's fictional land of Númenor, that's no coincidence; Ys and Lyonesse were part of the inspiration for Tolkien's doomed kingdom of the Second Age of Middle Earth.
The less-famous Kingdom of Cantre'r Gwaelod has some striking parallels. Originally made up of a broad, fertile valley west of Wales, the land was swallowed up by the sea and now lies beneath Cardigan Bay. Instead of the sinfulness that did in Ys, Lyonesse, and Númenor, Cantre'r Gwaelod was supposedly destroyed by negligence; in the Black Book of Carmarthen, a thirteenth-century document that is the earliest surviving manuscript written entirely in Welsh, the unfortunate kingdom met its doom because a maiden named Mererid who had been tasked with tending a well fell asleep, and the well overflowed and flooded the entire land.
What, exactly, Mererid was supposed to do about a well that was flowing so fast that it could inundate a whole country while someone was taking an afternoon nap is uncertain. But in the legend, the poor girl got the blame, and so the matter has stood.
But what separates Cantre'r Gwaelod from other lost-lands myths, including the most famous one -- Atlantis -- is that the Welsh version may actually have some basis in fact.
Two researchers, Simon Haslett, Professor of Physical Geography at Swansea University, and David Willis, Professor of Celtic History at the University of Oxford, found evidence on one of the earliest maps of Great Britain of two low-lying islands in what is now Cardigan Bay. The document, called the Gough Map after its last owner prior to its donation to the Bodleian Library at Oxford, dates back to the fourteenth century, although many historians believe it to be a copy of an earlier map. And it indicates that parts of Cardigan Bay were once dry land, and further, that the contours and terrain of these islands are reminiscent of the descriptions of Cantre'r Gwaelod from the Black Book of Carmarthen:
This study investigates historical sources, alongside geological and bathymetric evidence, and proposes a model of post-glacial coastal evolution that provides an explanation for the ‘lost’ islands and a hypothetical framework for future research: (1) during the Pleistocene, Irish Sea ice occupied the area from the north and west, and Welsh ice from the east, (2) a landscape of unconsolidated Pleistocene deposits developed seaward of a relict pre-Quaternary cliffline with a land surface up to ca. 30 m above present sea-level, (3) erosion proceeded along the lines of a template provided by a retreating shoreline affected by Holocene sea-level rise, shore-normal rivers, and surface run-off from the relict cliffline and interfluves, (4) dissection established islands occupying cores of the depositional landscape, and (5) continued down-wearing, marginal erosion and marine inundation(s) removed the two remaining islands by the 16th century. Literary evidence and folklore traditions provide support in that Cardigan Bay is associated with the ‘lost’ lowland of Cantre’r Gwaelod.
So it looks like we may have here another example of a legend with some basis in fact. A good many of the inundation myths -- including, very possibly, the Great Flood in the Bible -- might have come from the fact that at the end of the last Ice Age, the seas were rising, and previously dry land such as Beringia (between Russia and Alaska) and Doggerland (between England and continental Europe) were drowned. Cantre'r Gwaelod, perhaps, was a victim of the same sea level rise -- but unlike the others, we appear to have a map showing exactly where it lay.
And maybe once and for all we can absolve poor Mererid of any responsibility for its demise.