 This territory was known as Rhwng Gwy a Hafren, located between the Rivers Wye and Severn.They founded the castles of "Dinieithon", near present Llandrindod Wells, and "Cymaron" in Maelienydd, located between Llanbister and Llangunllo.A century later, after the collapse of Norman authority, the descendants of Mortimer were eventually expelled from this territory by the Cynllibiwg rebellion of 1148.