Two weeks after Congress withdrew to safer Maryland, Washington crossed the ice-choked Delaware River about 30 miles upriver from Philadelphia on the night of December 25–26, 1776. His approach over frozen trails surprised Hessian Colonel Johann Rall. The Continentals overwhelmed the Hessian garrison at Trenton, New Jersey, and took 900 prisoners. The celebrated victory rescued the American army's flagging morale, gave new hope to the Patriot cause, and dispelled much of the fear of professional Hessian "mercenaries". Cornwallis marched to retake Trenton but was repulsed at the Battle of the Assunpink Creek; in the night of January 2, Washington outmaneuvered Cornwallis and defeated his rearguard in the Battle of Princeton the following day. The two victories helped to convince the French that the Americans were worthy military allies.