The "High Water Mark of the Confederacy" reached via "Pickett's charge" as remembered here:
At 1 o'clock, two guns stationed in the Peach Orchard fired the signal to begin the bombardment. Over 150 Confederate guns on Seminary Ridge simultaneously exploded, sending shot and shell toward Cemetery Ridge. Startled Union artillerymen sprang to their guns and soon both ridges were covered with thick, acrid smoke. The pounding of the guns in the great duel shook the earth for nearly an hour, when the Union fire finally slackened. Longstreet reluctantly gave the order for the infantry to advance and nearly 12,000 Confederate soldiers began the long march toward the Union line. Suddenly the Union artillery came back to life, blasting the formations and cutting large swaths through them. As they reached the Emmitsburg Road, they were startled by the blast from hundreds of Union muskets. Officers were replaced by captains and sergeants, urging the men on until they reached "the Angle". Brig. General Lewis Armistead, the lone unscathed general of Pickett's Division, pierced the Union center with about 300 men. This was the "High Water Mark" and the last great Confederate gamble for victory.Only when you walk the ground between the lines do you understand the courage of that charge. And the great defense against it.
Photo from here of a reenactment.