It was founded by the Lord Rhys, Rhys ap Gruffydd in 1156, in response to a threat to his lands from the north from Owain Gwynedd, who had assembled an army to march on Ceredigion. Rhys “raised a ditch to give battle”, according to Brut y Tywysogion, or the ‘Chronicles of the Princes’.
The threat did not arrive but an earthwork castle was built on the site. A motte was constructed at the end of a low ridge running across marshy ground, surrounded on two sides by the confluence of the Dyfi and Einion rivers. The mound is still around 20 feet high with a diameter at the top of about 30 feet and it was surrounded by a deep ditch.
Roger de Clare, a Norman lord, attacked and captured the castle in about 1158. However, the Lord Rhys recaptured the castle. Llywelyn the Last held an assembly at Aberdyfi Castle in 1216 where he granted Welsh land in south Wales to other princes in return for their homage.