The remainder of the building is a Jacobean accretion made of brick and completely modernized. Gilbert de Clare built a Castle at Caerdigan, Pembrokeshire, Wales. A marriage brought it into the hands of William Marshall, who soon controlled the strongest castles on the peninsula. The keep has been transformed into a modern house. Of all the castles that finally came into William Marshall's possession, this was the most important to the area.
Scholars believe there is evidence that it was originally built of wood.
He sided with the Barons against King John, and his Castle at Tonbridge was taken. On 9 November 1215 he was one of the commissioners who, on the part of the Barons, was to treat of peace with the King. He died between 3 October and 28 November 1217. He married Amicia, Countess of Gloucester, second daughter of William FitzRobert, Earl of Gloucester, and his wife, Hawise, daughter of Robert de Beaumont, Earl of Leicester. Appreciation is expressed to Reed M. W. Wurts, one of the Heralds of the Society for furnishing the Baron's Shield on this page.