Cyfoesi Myrddin a Gwenddydd ei Chwaer

[2] Myrddin, the legendary 6th-century North British bard and warrior, is depicted as being encouraged by his sister Gwenddydd to utter a series of prophecies detailing the future history of the kings of Gwynedd, leading up to an apocalyptic ending.

[7][8] Cyfoesi Myrddin a Gwenddydd ei Chwaer survives in two manuscripts: the Red Book of Hergest (Oxford, Jesus College, MS 111), which dates from the last quarter of the 14th century or the first quarter of the 15th; and Aberystwyth, National Library of Wales, MS Peniarth 20, which dates from the first half of the 14th century.

Oliver Padel cast doubt on the linguistic evidence for an early date and suggested that it could have been written about the middle of the 12th century or a little later.

[5][11][12] John Bollard rejected the theory that the poem had grown by accretion and instead assigned it to the 13th century, while acknowledging that it made use of much older traditions.

[4] The figure of Myrddin may be identical with a madman called Lailoken who appears in Jocelyn of Furness's Life of St Kentigern.