The first engagement of July 3rd began in the small hours of the morning before dawn. Slocum attacked Culp's Hill in an effort to regain Confederate control of the area to the north. The battle raged on until mid-morning when the Confederates were forced to retreat across Rock Creek.

From the Confederate line on Seminary Ridge, Generals Lee, Longstreet and Pickett made plans for a 12,500 man attack to the Federals center position. The attack was preceded with a bombardment of Federal lines which began at 1:00 P.M. using some 140 Confederate cannons. The Federals responded with their own artillery with an exchange lasting until about 2:00 P.M. when they slowed their fire in a ruse to make the Confederates think that they were out of artillery resources. With this, the Confederates left the woods of Seminary Ridge at 3:00 P.M. and formed ranks for a frontal assault. The colors of forty-two Confederate regiments began the march across the plain which separates Seminary and Cemetery Ridge with the objective being the now famous "copse of trees" which marked the center of the Federal lines. When the Confederates reached the Emmitsburg Road, Federal forces resumed their artillery fire blasting large holes in the advancing lines.

The Confederate line suffered incredible losses, but continued to advance. Brigadier General Lewis Armistead, his hat on his sword, led about 300 of his men in a "rebel yell" over the stone wall at the battery of Colonel Alonzo Cushing who laid dead. Within moments of crossing the wall, Armistead himself was mortally wounded. Among historians, this is considered the "high water mark" of the Confederate cause. The attacked had failed.

Of the force of 12,500 Confederates who crossed the corn field, only 5,000 returned. Only 800 of Pickett's 5,000 man force reported for duty the next day. In the three days of fighting, the Federal army lost 23,000 men and the Confederates losses numbered 28,000.