 Once on the other side, the King and his men stormed into the town, trapping Matilda in the castle.Oxford Castle was a powerful fortress and, rather than storming it, Stephen decided to settle down for a long siege.Just before Christmas, Matilda sneaked out of the castle with a handful of knights (probably via a postern gate), crossed the icy river and made her escape past the royal army on foot to Abingdon-on-Thames and then riding to safety at Wallingford, leaving the castle garrison to surrender the next day.