Burnside's plan, approved by Lincoln, was to move the army south to attack Richmond. He decided to move via Fredericksburg. That way he could depend on the Union Navy to keep him supplied instead of overland supply which could be attacked by Confederate cavalry. He would also sidestep the Confederate army and get between them and Richmond. His main base was the landing at Aquia Creek. His plan was to use pontoon bridges to cross the Rappahannock at Fredericksburg. But the pontoon bridges were two weeks late in arriving. So the Army of the Potomac sat across the river and waited. This delay gave Lee ample time to gather his forces to oppose Burnside, who had now lost the advantage of surprise. During the early morning hours on December 11, soldiers assembled the pontoon bridges so the army could cross. The confederates fired on them causing delays in completing the bridges. Burnside's 150 artillery pieces opened fire from Stafford Heights. The shells did extensive damage to the town but did not drive off the Confederates. Finally the bridges were completed late that evening. More than 120,000 Union troops poured across the bridges into Fredericksburg. Lee continued to give token resistance to allow General Stonewall Jackson's corps time to get in place and complete a Confederate line some three miles long.