In the late 11th century AD William I granted land along the Welsh borders (Marches) to powerful Norman earls. Known as the Marcher Lords, these earls built a string of castles from Chester in the north to Chepstow in the south and Pembroke in the west and used them as bases from which to take land on the Welsh side of the border. The Marcher Lords were favoured agents of the English monarchs, chosen for their trustworthiness. This was important, as they were not subject to English law, but could run their lands however they wished and could maintain private armies. They were so powerful that the English kings were often worried that they would rebel against the Crown.

A good example of how the English nobility came to power in Wales is William Marshal (1146-1219) who, though not noble by birth, rose through knightly prowess and political acumen to become a loyal adviser of four Plantagenet kings. Henry II (reigned 1154-1189) granted him land in south Wales and made him earl of Pembroke and Striguil (Chepstow). All Marshal’s sons died without heirs and in the 1260s Henry III gave the land and titles of Pembroke to his half-brother William de Valence.