Castell y Bere was built in the 1220s by Llywelyn the Great on a rocky hillock overlooking the Dysynni Valley, near Llanfihangel-y-pennant. Traditionally the Welsh princes had not constructed castles, instead using undefended palaces called "llysoedd", or courts. From the late 11th century onwards, the Normans had advanced into Wales, taking lands in the north and establishing a band of occupied territory in the south called the Welsh Marches. During the 12th century some timber and earthwork castles began to be built, but in small numbers.