{{Short description|Welsh medieval commote}} {{Use dmy dates|date=April 2022}} {{infobox historic subdivision |capital = Cefnllys Castle |status_text = Maelienydd |image_map = Map of the Cantrefs and Commotes of Rhwng Gwy a Hafren.svg |image_map_caption = Shown within Rhwng Gwy a Hafren |coordinates = {{coord|52|15|21.2|N|3|20|24.7|W|type:adm3rd_region:GB|display=inline,title}} |era = Medieval |today = Powys, Wales }}
{{langnf|cy|'''Dinieithon'''|fort on the River Ieithon|italic=no|paren=left}}; also known as '''Dineithon''' or '''Cefnllys''') was a commote within the cantref of Maelienydd, in the medieval region of Rhwng Gwy a Hafren in Wales. It was situated near the modern town of Llandrindod Wells.
The southernmost of the four commotes in Maelienydd, it was also the most important due to its arable land and the presence of the region's administrative centre at Cefnllys. It bordered Gwrtheyrnion to the west and Elfael to the south.
Dinieithon was probably part of the Kingdom of Powys in the Early Middle Ages. In 1093, the Norman barons Roger de Montgomery, Ranulph de Mortimer, and Philip de Braose conquered the region, and Ralph Mortimer built a motte-and-bailey at Dinieithon to secure his new territory.<ref>{{cite journal |last1=Remfry |first1=Paul Martin |title=Discovering the lost kingdom of Radnor |journal=British Archaeology |date=May 1998 |volume=34 |url=http://www.archaeologyuk.org/ba/ba34/ba34feat.html |archive-url=https://web.archive.org/web/20160416122340/http://www.archaeologyuk.org/ba/ba34/ba34feat.html#remfry |archive-date=16 April 2016 |accessdate=24 September 2020 |issn=1357-4442 }}</ref> The native Welsh made a recovery in the area, until Ralph Mortimer II built a masonry castle at Cefnllys, which subsequently became seat of the cantref.<ref>{{cite journal |last1=Brown |first1=A. E. |title=The castle, borough and park of Cefnllys |journal=The Radnorshire Society Transactions |date=1972 |volume=42 |page=12 |url=https://journals.library.wales/view/1191402/1194939/12 |accessdate=14 September 2020}}</ref> thumb|150px|left|alt=Map of medieval Wales|Map of commotes Like the rest of Maelienydd, it became part of Radnorshire as part of the Laws in Wales Acts 1535–1542.
==See also== *Maelienydd *Cefnllys Castle
==References== {{reflist}}
Category:Commotes Category:History of Powys
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