As had been ordered by A. P. Hill the night before, the Confederate division under Harry Heth began advancing towards Gettysburg at 5:00 am. Approaching the town from the north, they encountered Union troopers from John Buford's command at 7:30 am. The rebel skirmishers pushed forward until they reached the main Union line, on McPherson's Ridge just north of town. It was clear the Confederates would need to deploy more than a few skirmishers to make it into Gettysburg. Heth deployed Archer's and Davis's brigades on Herr Ridge opposite the Union positions. They pushed towards McPherson Woods, supported by cannon fire. Their advance was slow. The Federal dismounted cavalry carried breechloading carbines which could be reloaded much faster than the rifles the infantry carried, but the Union line was much thinner. They grudgingly gave ground, slowly retiring. They held off the Confederate advance for two hours. As Archer's brigade crested the hill, thinking that they were finally really driving the Union cavalry, the sighted a line of Federal infantry. Reynold's I Corps had arrived.
John Reynolds of Pennsylvania was a gallant officer with battlefield experience and one of the most skilled generals in the army. His men had begun their march that morning. They didn't know they were going into a serious battle, they thought they were just there to support Buford in a cavalry skirmish. At the head of the First Corps were some of the best troops in the Army of the Potomac, including the Iron Brigade, known for their black Hardee Hats and hard fighting proven on many fields. When Reynolds arrived in Gettysburg ahead of his troops he was informed of the situation. Knowing that his friend Meade would be willing to fight Lee, he decided to hold the high ground north of Gettysburg. If necessary he could fall back to Cemetery Hill, a strong position just south of town. He told Buford to hold on until his infantry arrived to take over, and sent an order to O. O. Howard to move his 11th Corps to Gettysburg.