In 1189 William Marshal became Earl of Pembroke and the castle passed into his hands. Over the next 30 years he transformed the earth and timber structure into a powerful stone fortification.
William Marshal was a mighty figure in mediaeval Britain. A crusader and faithful adherent of Henry II, he championed the causes of both Richard I and John, whom he advised on the Magna Carta. He was also Regent to the infant Henry III. His chief legacy to Pembroke was the Great Tower and much of the Inner Ward. William was succeeded by each of his five sons in turn. His third son, Gilbert, was responsible for enlarging and strengthening the castle between 1234 and 1241.