edmund, the earl of lancaster and the "capitaneus" of the royal forces in wales, was given the three castles in 1267 and for many centuries they were held by the earldom, later duchy, of lancaster. king edward i's conquest of wales in 1282 removed much of white castle's military utility, although it continued to be used in the administration of the surrounding manor, and for mustering military levies. little further work was carried out on the fortification, although one of the gatehouse towers was repaired at some point, and repairs were carried out to the chapel tower and gatehouse under king henry vi. by 1538, white castle had fallen into disuse and then into ruin; a 1613 description noted that it was "ruynous and decayed".