Constructed by Llywelyn the Great in the 1220s, the stone castle was intended to maintain his authority over the local people and to defend the south-west part of the princedom of Gwynedd. In 1282 war with Edward I of England resulted in the death of Llywelyn’s grandson, Llywelyn ap Gruffudd, and Castell y Bere fell to English forces.
Edward I expanded the castle further and established a small town beside it. In 1294 the Welsh leader Madoc ap Llywelyn mounted a major revolt and the castle was besieged and apparently burnt. Edward did not repair it and it became ruined.