In December, Longstreet's First Corps played the decisive role in the Battle of Fredericksburg, midway between the two opposing capitals, where the Confederate army made its stand to protect Richmond from the Army of the Potomac, now commanded by Ambrose Burnside. Since Lee moved Longstreet to Fredericksburg early, it allowed Longstreet to take the time to dig in portions of his line, methodically site artillery, and set up a kill zone over the axis of advance he thought the Union attack would follow. Remembering the slaughter at Antietam, in which the Confederates did not build defensive works, Longstreet ordered trenches, abatis, and fieldworks to be constructed south of the town along a stonewall at the foot of Marye's Heights, which would set a precedent for future defensive battles by the Army of Northern Virginia. This was completed in the days before the battle. After failing to cross the Rappahannock on December 11, Burnside ordered an artillery bombardment of the town, and forced his way across the following day.