The castle became more important as an administrative centre during John's reign, and he visited the castle 51 times. During the First Barons' War, the castellan joined the rebels in their struggle against John. William Marshal besieged Marlborough Castle in 1217, by which point John was already dead, and captured it for the royalist cause. According to History of William the Marshall, William Marshal (the father of the William who besieged Marlborough) gave orders to demolish (slight) castles captured from the rebels.
