After a series of victories in northern Virginia, Lee led his army through the Shenandoah Valley to begin his second invasion of the North. The first day was a meeting engagement as the two armies collided.  Initially, the Union defended the low ridges northwest of the town with cavalry joined later by infantry, but these forces collapsed under assaults by two Confederate corps.  Lee did not press his advantage and Union forces retreated through the streets of the town to the hills just to the south.  Here as both armies assembled, the Union laid out a defensive formation resembling a fishhook. In the late afternoon of July 2, Lee launched a heavy assault on the Union left flank, and fierce fighting raged at Little Round Top, the Wheatfield, Devil’s Den, and the Peach Orchard. On the Union right, Confederate demonstrations escalated into full-scale assaults on Culp’s Hill and Cemetery Hill. All across the battlefield, despite significant losses, the Union defenders held their lines.  On day three, fighting resumed on Culp’s Hill, and cavalry battles raged to the east and south, but the main action was a dramatic infantry assault by 12,500 Confederates against the center of the Union line on Cemetery Ridge, known as Pickett’s Charge. The charge was repulsed by Union rifle and artillery fire, at great loss to the Confederate army.  Meade allowed Lee’s forces to retreat back to Virginia.