The "Triads of the Island of Britain" (also known as the "Welsh Triads") 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 (also called Alan Fyrgan) and Iron Age characters such as Caswallawn (Cassivellaunus) and Caradoc (Caratacus).