 William's father, John Marshal, supported King Stephen when he took the throne in 1135, but in about 1139 he changed sides to support the Empress Matilda in the civil war of succession between her and Stephen which led to the collapse of England into "the Anarchy".When King Stephen besieged Newbury Castle in 1152, according to William's biographer, he used the young William as a hostage to ensure that John kept his promise to surrender the castle.John, however, used the time allotted to reinforce the castle and to alert Matilda's forces.