Castell y Bere is a Welsh castle near Llanfihangel-y-pennant in Gwynedd, Wales. 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.