Seisyllwg
Digital Passport
Nomenclature and Geography
Category: Historical
Summary
Seisyllwg was a medieval Welsh kingdom originating from Ceredigion and Ystrad Tywi. It emerged as a distinct unit, though its exact origins are unclear, and was named after King Seisyll of Ceredigion. In 920, Hywel Dda merged Seisyllwg with Dyfed, forming the kingdom of Deheubarth.