 The army moved to Falmouth, Virginia, where Burnside spent weeks orchestrating his attack on Fredericksburg just across the Rappahannock River.The Army of the Potomac, having constructed pontoon bridges across the Rappahannock, commenced the Battle of Fredericksburg on the morning of December 13, 1862.The Confederate army occupied the city of Fredericksburg and a high ridge behind the city known as Marye's Heights.