The Coelbren y Beirdd (English: "Bards' alphabet") is a runic alphabet system created in the late eighteenth century by the literary forger Edward Williams, best known as Iolo Morganwg.
The alphabet system consisted of twenty letters and twenty other representations of elongated vowels that resembled Ancient Greek and could be carved on four-sided pieces of wood and fitted into a frame he called a "peithynen". Williams presented wooden druidic alphabets to friends and notables, and succeeded in persuading many of its authenticity.
A Welsh Bardic and Druidic essay, written by his son Taliesin Williams and published as a pamphlet in 1840, defended the authenticity of the alphabet and won the Abergavenny Eisteddfod in 1838.
Taliesin Williams's book was written about other Coelbrennau'r Beirdd, which is the name of a Welsh language manuscript in the Iolo Manuscripts and two manuscripts in Barddas, one with the subtitle "yn dorredig a chyllell". Iolo Morganwg suggested they were originally the work of bards from Glamorgan who had their manuscripts copied into collections stored at Plas y Fan, Neath Abbey, Margam Abbey and Raglan Library, and compiled by Meurig Dafydd and Lewys Morgannwg, amongst others, in the 1700s. These were suggested to have again been transcribed by Edward Dafydd, John Bradford and Llywelyn Siôn. Moganwg suggested that he had collected some of Siôn and Bradford's manuscripts, while the majority, including all of Lewys Morgannwg's sources, were lost. This claim to authenticity has been questioned by numerous scholars such as Glyn Cothi Lewis.