Two versions of an ancient tale.
In one version of the story, popular in Victorian times, the job of closing the sluices fell to the watchman Seithenyn. One night, after a celebratory feast, a storm blew up from the south west and drove the tide against the dykes. Seithenyn had fallen asleep through too much drink, and had forgotten to close them, and the land was drowned.
But an older version of the story is recalled in fragmentary fashion in the poem Boddi Maes Gwyddno, to be found in the Black Book of Carmarthen. This tells, perhaps, that Seithenyn was a visiting king who was attracted to the “well cup-bearer” Mererid. Perhaps it was she who was in charge of the sluices. Seithenyn, drunk after the feast, prevented her from attending to her duties, and so the sea flooded in. The poem vividly describes her lament:
Diaspad vererid y ar vann caer.
hid ar duu y dodir.
gnaud guydi traha trangc hir.
Mererid’s cry from the city’s heights
Reaches even God.
After pride comes a long ending.
The remains of the dykes which defended the Cantref can still be seen today: Sarn Badrig reaches out into the sea near Barmouth, and Sarn Gynfelyn between Clarach and Borth.