Welsh Triads

The Welsh Triads (Welsh: Trioedd Ynys Prydein, "Triads of the Island of Britain") are a group of related texts in medieval manuscripts which preserve fragments of Welsh folklore, mythology and traditional history in groups of three. The triad is a rhetorical form whereby objects are grouped together in threes, with a heading indicating the point of likeness; for example, "Three things not easily restrained, the flow of a torrent, the flight of an arrow, and the tongue of a fool."

The texts include references to King Arthur and other semi-historical characters from Sub-Roman Britain, mythic figures such as Brân the Blessed, undeniably historical personages such as Alan IV, Duke of Brittany (who is called Alan Fyrgan) and Iron Age characters such as Caswallawn (Cassivellaunus) and Caradoc (Caratacus).

Some triads simply give a list of three characters with something in common (such as "the three frivolous bards of the island of Britain") while others include substantial narrative explanation. The triad form probably originated amongst the Welsh bards or poets as a mnemonic aid in composing their poems and stories, and later became a rhetorical device of Welsh literature. The Medieval Welsh tale Culhwch and Olwen has many triads embedded in its narrative.

The earliest surviving collection of the Welsh Triads is bound in the manuscript Peniarth 16, now at the National Library of Wales, which has been dated to the third quarter of the 13th century and contains 46 of the 96 triads collated by Rachel Bromwich. Other important manuscripts include Peniarth 45 (written about 1275), and the pair White Book of Rhydderch (Welsh: Llyfr Gwyn Rhydderch) and Red Book of Hergest (Welsh: Llyfr Coch Hergest), which share a common version clearly different from the version behind the collections in the Peniarth manuscripts.

...
Wikipedia