In the summer of 1863, Confederate Gen. Robert E. Lee launched his second invasion of the Northern states. Lee sought to capitalize on recent Confederate victories and defeat the Union army on Northern soil, which he hoped would force the Lincoln administration to negotiate for peace. Lee also sought to take the war out of the ravaged Virginia farmland and gather supplies for his Army of Northern Virginia. Using the Shenandoah Valley as cover for his army, Lee was pursued first by Union Maj. Gen. Joseph Hooker, and then by Maj. Gen. George G. Meade, who replaced Hooker in late June. Lee's army crossed into Pennsylvania mid-June, and by June 29th had reached the Susquehanna River opposite Harrisburg and at Wrightsville. The opposing forces collided at the crossroads town of Gettysburg, Pennsylvania, on the morning of July 1st. In severe fighting, the Confederates swept the Federals from the fields west and north of town, but were unable to secure Cemetery Hill and Culp's Hill to the south. The following day, as reenforcements arrived on both sides, Lee attacked the Federals on the heights, and also Little Round Top further south, but failed to dislodge the defenders. On July 3rd, Lee attacked the Union center on Cemetery Ridge and was repulsed in what is now known as Pickett’s Charge. Lee's second invasion of the North had failed, and had resulted in heavy casualties on both sides. An estimated 51,000 soldiers were killed, wounded, captured, or listed as missing after the Battle of Gettysburg.