Thrice Prydwen's freight went we to Caer Sidi,
Thence but seven did we regain our country.'
The same couplet, slightly modified to suit the rhyme, closes the remaining six stanzas of the poem, with the exception of the last, which ends with a short prayer; and we know from another poem[1] in the same manuscript that Caer Sidi was in a mythical country beneath the waves of the sea. Pryderi and his father Pwyll Head of Hades have already been mentioned, though it is not evident who was meant by their apostle or messenger; but it may be guessed that it was the porter of Hades. His masters, however, could not be expected to have treated Gweir with tenderness in case he should prove to have been Gwydion; and here it may be asked why Gweir should be supposed to have been Gwydion. Now Gweir son of Gweiryoeᵭ occurs in one of the Triads, where he is called one of the Three Paramount Prisoners of the Isle of Britain, the other two being Llûᵭ[2] and Mabon (p. 28), both gods of the pagan Celts; and we seem to be warranted in assuming Gweir to have been of similar rank. But it is right to mention, as an instance of Arthur's intrusion, that, in spite of the triadic arrangement, his name is here added as that of a fourth and greater prisoner than the other three. The triad referred to is found in one of the collections in the Red Book of Hergest, a Jesus College manuscript of the thirteenth and fourteenth centuries; but it occurs in a brief and presumably old form in an earlier group in
