On this day in 1863, America’s bloodiest battle began at Gettysburg.

During this first day, General Lee urgently concentrated the Confederate forces at Gettysburg to engage and defeat the Union Cavalry. General Henry Heth led the Confederate division, which began the march into Gettysburg on July 1, 1863. Their quest to conquer the territory and seize supplies halted when they found resistance from three brigades of Union cavalry.

Brigadier General John Buford of the Union cavalry led the Brigade that delayed General Henry Heth's entry into Gettysburg as they waited for reinforcements to arrive. At about 11:00 AM, John F. Reynolds's I corps arrived to reinforce a counterattack that left casualties on both sides.

This attack slowed the Confederate advance. However, the infantry of Confederate reinforcements under generals Richard Ewell and A.P. Hill overwhelmed the Union lines. 24,000 Confederates faced 19,000 Federals, collapsing the hastily developed Union lines and forcing the Union defense line back to Cemetery Hill. The Confederate hesitated to attack Cemetery Hill because they were uncertain about the enemy's actual dispositions.

General Winfield Scott Hancock arrived at about 4:00 PM to assess Meade's situation. He concluded that Gettysburg was the place to fight. He ordered III Corps and XII Corps under Generals Daniel Sickles and Henry Slocum forward.