Previous to this battle and the battle at Antietam, Maryland the year before, Lee had great success in battle, though at the cost of high casualty rates. His success rate had been so high, he'd thought himself nearly-invincible. It is perhaps because of this, and high morale among his men, that he shrugged off suggestions to withdraw from recently-captured Gettysburg to find ground more favorable to Confederate troops.
The battle, known as the High Water Mark of the confederacy, began when Confederate soldiers attacked a Union cavalry division west of town. Even though they were outnumbered, Union forces held off the attack. They were eventually driven back through by Confederate reinforcements, and many Union soldiers were captured in the ensuing chaos. During the night, the union troops built up defenses as the remainder of the army arrived.
By the next morning, Union and Confederate troops took up positions on two opposing ridges, nearly a mile apart. Lee ordered an attack on both Union flanks. On the south end, Confederates broke through union lines leaving so many dead and wounded the area is now known as Bloody Run, and left the rocky area called Devil's Den at Little Round Top in chaos. In the north, the Confederates took Culps Hll on one occasion, but eventually the attack was futile. Southern troops were in-fact very close to Northern supply trains, and additional assistance was available. But due to communication problems, both of these opportunities were missed.
On the final day of battle, Lee attempted to attack the middle of Union lines. Both sides made a spectacular display of the power of their artillery, but it didn't weaken the Union battle lines. Eventually, General George E. Pickett made a final attempt to recapture some of the previous day's successes. Fifteen hundred infantry troops crossed the open field toward the Union lines. In 50 minutes, they managed to cross the mile between the ridges, even while being cut down by artillery and rifle fire. They reached the Union line, but did not break it. In the 50 minutes of the Pickett's Charge, two-thirds of men had become casualties. Lee's army retreated the next day.
There were around 51,000 casualties on both sides in addition to 5,000 dead horses and almost 600 tons of expended ammunition. Add to that the 172,000 men and 600 cannons that had torn through the landscape for three days of horrific battle, and the landscape was reduced to a hellish scene of devastation with bodies needing to be disposed of quickly due to the summer heat. Four months later, when Lincoln arrived to mark the dedication of the location as a National cemetary, the landscape was still scarred from the epic battle.
The eventual end result of the battle was that Lee made no more offensive moves toward the north, in fact, he remained on the defensive for the remainder of the war. Any hopes that the Confederacy had of either recognition of their state by other nations, or of bringing about a truce favorable to the Southern cause were lost.
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