During the summer of 1142 Robert returned to Normandy to assist Geoffrey with operations against some of Stephen's remaining followers there, before returning in the autumn. Matilda came under increased pressure from Stephen's forces and was surrounded at Oxford. Oxford was a secure town, protected by walls and the River Isis, but Stephen led a sudden attack across the river, leading the charge and swimming part of the way. 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. Matilda and her companions reportedly wore white to camouflage themselves against the snow.