In the second branch of the Mabinogion, King Bendigeidfran and his men travel from Britain ("the Island of the Mighty", or Ynys Y Kedeirn), intent on avenging the punishment of his sister, Branwen, at the hands of the Irish (which takes place against the will of the Irish king Matholwch).

It is written that

Bendigeidfran, and the aforementioned hosting sailed towards Ireland. The ocean was not extensive [back] then: he went by wading. There used to be nothing except two rivers called the Lli and the Archen. And after that the ocean spread out, and the sea flooded the kingdoms. Then he advanced, carrying all the string-minstrels on his back, making for the land of Ireland.

Bendigeidfran was a giant, and so it was easy for him to cross, though the rivers were too deep for normal men to cross (he looks like a mountain from afar).

Why did the Lli and Archen rivers flood, creating an ocean (which we today call the Irish Sea)? The two are never mentioned again in the Mabinogion (I checked the three other branches), and Bendigeidfran soon drops out of the story (I won't spoil the reason why), so giants crossing rivers are not involved.

As a side note, the rivers seem purely fictional; I do not know if they show up in any other legends, though.

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    It is probably a memory from the variations of ice in the region. In ice ages a lot of the water of the ocean is tied up in ice and the whole area was one land mass. As the ice melted the waters would come back and called "rivers". en.wikipedia.org/wiki/British_Isles
    – anna v
    May 8, 2015 at 3:57
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    @annav I don't think that really makes any sense... I'd guess the most recent ice age would have ended a significant amount of time before this story was written.
    – Daft
    May 8, 2015 at 10:28
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    written most probably, but the link gives ice 5000 years agoo, and mythologies start orally
    – anna v
    May 8, 2015 at 10:31
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    @annav The stories are generally given as relatively recent (obviously pre-1000 AD), but not 5000 years ago.
    – HDE 226868
    May 8, 2015 at 17:41
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    Many people believe that the Noahs Ark myth is based on the black sea flooding somewhere 7000-5000 BC, so why shouldn't this tale have it's roots in a flooding from 5000-4000 BC? May 10, 2015 at 20:29

1 Answer 1


It is interesting to note that these rivers, as well as other sunken places, are mentioned in Patrick Sims-Williams's Irish Influence on Medieval Welsh Literature, p192ff. (Findable at Google Books.)

The chapter mentions other places that seem to have been known dry land locations that had flooded within historical or literary memory (one got uncovered just this year). While it seems clear that early authors were aware of land being inundated, I'd not be surprised if there weren't some memories of late glaciation Europe at work here. Both Wales and Ireland were bigger even as late as a few millennia BC.

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