Coelbren y Beirdd was a false alphabet invented by Iolo Morganwg around 1791. He claimed that it was the alphabet of the Celtic druids and that it had 20 'letters' and 20 others to represent elongated vowels and mutations. It would be hewn on a four-sided piece of wood and these pieces of wood would be placed in a frame, so that each piece could be turned to read all four sides. The name for this 'book' was peithynen.
Taliesin ab Iolo published a book, Coelbren y Beirdd, based on his father's manuscripts, in 1840. The alphabet was popular with some poets and druids throughout the nineteenth century although others, such as Edward (Celtic) Davies (1756-1831), questioned its authenticity. By 1893 J. Romilly Allen, joint-editor of Archaeologia Cambrensis', comments in a letter to the Herald Bard:
'I think the so-called Bardic Alphabet a gigantic fraud - I don't believe you will find it repay you to look at these bogus alphabets and pseudo-Druidic antiquities as anything but but (sic) the most bare faced impostures.'