On Day 2 at Gettysburg, the great battle between north and south was brutally contested at the south and at the north.

To call Cemetery Ridge a ridge is fairly generous. It’s a mild undulation in the Pennsylvania farmland, maybe two miles long, looking west over open fields down to a line of woods about a mile away. But on either end of the ridge, things get a little more dramatic. At its south end, the ridge rises about 100 feet to a pair of hills, the higher one topped by trees and the closer, lower one, studded by boulders. Unnamed at the time, they would come to be known as Big Round Top and Little Round Top. And at its north end, as the ridge approaches the town of Gettysburg, it swings suddenly around to the east, and connects with a small wooded rise called Culp’s Hill. On July 2, 1863, Union commander George Gordon Meade and his subordinate Winfield Scott Hancock stood at the middle of this fishhook-shaped line, trying to guess what point Robert E. Lee might strike first.

The answer was frightening: both ends, and simultaneously.

To the south, Lee sent his forces into the Union’s left flank, in an attempt to gain the high ground and roll up along Cemetery Ridge. But a mistake by a northern general proved to be a blessing. A large force of Union soldiers had foolishly moved forward, down off Cemetery Ridge to the flatter lands below, and Lee’s forces ran into them unexpectedly. In places history colorfully recalls as the Wheatfield, Plum Run Valley, the Peach Orchard – and more grimly, the Devil’s Den – the federals slowed Lee’s advance. This delay gave Meade time to realize that his left flank was thinly manned and exposed, and he moved much of his force from his center and right to reinforce it. The reinforcements arrived just in time, and the northern cause was saved by not one but two suicidal bayonet charges. On Little Round Top, the 20th Maine, having run out of ammunition, charged downhill into the rebels, scattering their forces and stopping their advance. And near the crest of Cemetery Ridge, Hancock ordered the 1st Minnesota to suddenly charge forward, a desperate move that resulted in a staggering 80% casualty rate, but bought time for more union soldiers to arrive and secure the high ground. Hancock later recalled it as the bravest act of the entire war.

To the north, Lee sent a second force around and up Culp’s Hill, in an attempt to get behind the federal lines. And he picked a tender spot. With much of the Union forces shifted to reinforce the left flank, a single brigade of 1,350 Union soldiers was left to defend a half-mile-long section against the attack of an entire confederate division, numbering over 6,000. Luckily for the Union, their forces were led by George Green, a tough character who demonstrated his wisdom – he was the oldest Union general of the war, aged 62 – as well as his value as an engineer. Before the rebels attacked, his men had created a maze of breastworks that turned the confederate advance into a nightmare uphill battle through boulders and downed trees. Green’s defenses held long enough for reinforcements to arrive and stop the rebels just 400 yards from the Union army’s main supply lines.

Day 2 was a brutal day, an anxious day, and it came to a close with both ends of the Union line strained to the breaking point, but holding. When Meade and his generals came together, exhausted, on Cemetery Ridge to compare notes, it quickly became clear that Lee had committed nearly his entire army to the offensive. But there was one anxiety-producing exception. Throughout Day 1 and 2, no one had seen or heard anything about one of Lee’s most feared commanders.

Meade and Hancock were left to scratch their heads: where was confederate Major General George Pickett, and his division of 6,000 veteran rebel soldiers?…