A restored canon at a Union position along Cemetery Ridge points toward the battlefield at the Gettysburg National Military Park in Gettysburg, Pennsylvania. (TIM SLOAN/AFP/GETTY IMAGES)

It was the biggest battle of the war, unequaled in scale and violence by anything seen before or since on this continent. Two immense armies collided in the fields and orchards and woods around Gettysburg, Pa., on July 1, 1863, and fought for three days, full-bore, no quarter given, a massive smash-up that was arguably the pivotal moment of the great conflict that sits at the heart of American history.

Abraham Lincoln called what happened in Gettysburg “a new birth of freedom,” a phrase that chiseled its way into our national civic poetry and the wall of his memorial. The battle was also an epic slaughter, the bloodiest chapter in a fratricidal war. The National Park Service records 3,155 Union and 3,500 Confederate deaths over the three days, but some students of the battle believe that the Confederate death toll was much higher. Thousands more were mortally wounded. Casualties — including wounded, captured and missing — topped 50,000 for the two armies combined. By a wide margin, Gettysburg spilled more blood than any other Civil War engagement.

Lincoln’s famous address that November honored the men who stood their ground against a furious assault. But the story of Gettysburg, as we usually tell it today, wheels back to the other side of the field, to the Army of Northern Virginia, and its revered, almost sainted commander, Gen. Robert E. Lee. Because Gettysburg was Lee’s fatal blunder.

He ordered repeated assaults on fortified Union positions on high ground. What was Lee thinking? Could it have worked? Who was to blame for the failure? For a century and a half, historians and Civil War buffs have been gnawing on these questions.

This summer, the Park Service will not permit a reenactment of the battle as part of the sesquicentennial celebration. Park officials don’t want a replay of the events of 50 years ago, when reenactors tore up the battlefield and left it a mess. But they also think it would send the wrong signal and celebrate too much the martial element of the anniversary. Instead, there will be commemorative speeches and candle-lighting ceremonies, and on July 3, the public will be invited to walk in an orderly procession where Pickett’s division charged Cemetery Ridge.

The tide of war begins to turn in favor of the Union

The culmination of the battle will be marked not by fanfare but by a bugler playing a tune composed during the Civil War. The tune is known today as taps.

The first day

In June 1863, the Army of Northern Virginia crossed the Potomac River and kept going, through Maryland, into Pennsylvania. Lee had 75,000 men, eager to feast on the comparative bounty of Pennsylvania after so many months scavenging for food in war-torn Virginia. Beyond the need to find fresh supplies for his army and give Virginia agriculture a chance to recover, Lee had strategic goals. An invasion of the North might persuade northern Democrats to push for a peace treaty. Most of all, he was spoiling for a fight, hoping to lure the Union army into a confrontation in the North. He thought he could destroy that army and end the war.

Where would this great battle occur? No one knew — until it was already underway.

Lee’s mercurial head of cavalry, Gen. J.E.B. Stuart, had a tendency to wander off, and once again he’d gone gallivanting across the countryside, leaving his commander blind to the movements of the enemy. Unbeknown to Lee, the Army of the Potomac, with 90,000 men, had moved quickly north, headed his way.

On June 28, Lee learned from a spy about the Union advance. He also learned that Lincoln had changed generals again, putting the Army of the Potomac under Gen. George Meade. Lee ordered his scattered corps commanders to converge, but they weren’t supposed to bring on a major battle. A relatively small number of rebel soldiers looking for supplies — shoes, famously, though like so much else that’s a subject of debate — ventured toward the little town that served as the seat of Adams County. Gettysburg radiated roads to all points of the compass, and those roads became like plumbing that sluiced the two armies toward each other.

Union cavalry under the command of Gen. John Buford spotted a detachment of rebels coming east toward Gettysburg. Buford eyeballed the terrain, with several ridges running parallel. Buford decided to hold the ridges until he could be reinforced. Thus, it was Buford, thinking on his feet — or on his horse — who selected Gettysburg as a field of battle.

The first shot rang out at 7:30 a.m. July 1. The dismounted Union soldiers were on the verge of being overrun when help arrived under the command of Maj. Gen. John Reynolds. Today one of the most magnificent equestrian statues at Gettysburg shows Reynolds, facing west, near where a bullet killed him soon after he arrived at the scene.

Noted author Stephen W. Sears of Landscape Turned Red and Civil War buff Gene Thorp square off over Gen. George B. McClellan’s place in history.

This started to look like another rebel victory, a fitting follow-up to Lee’s smashing triumph at Chancellorsville two months earlier. Union forces fled through the town and regrouped on the high ground beyond, including Cemetery Hill. Lee hadn’t ordered up a major battle, but when he arrived at the edge of Gettysburg late in the day, he saw his opportunity. He ordered one of his three corps commanders, Gen. Richard Ewell, to press the attack and take the hills beyond the town “if practicable.” It was a discretionary order. Ewell decided that his men had fought enough for the day, and he did not try to take the high ground. This was a fatal hitch in the Confederate step. The Union soldiers dug in at Cemetery Hill and Culp’s Hill and along Cemetery Ridge.

That night, the campfires flared around Gettysburg as two huge armies tended to their dead and wounded and prepared to resume their war in the morning.

The second day

The battle, as it unfolded, was a sprawling affair, too big for anyone to keep track of it all. But in some ways, it was a simple set-piece battle, fairly easy to diagram after that first day. The Union line was shaped like an upside-down fishhook, relatively compact, with interior lines of movement that enabled rapid reinforcements from one side of the battle to the other. The rebels were stretched around that position in a looping, thin, five-mile line that made communication and reinforcement more difficult. And the Southerners would have to fight uphill much of the time.

Lee’s ace lieutenant, Gen. James Longstreet, recognized that his men had the inferior position, and he advised Lee to maneuver away from Gettysburg, to the south, toward Washington, where the rebels could take up a more favorable, defensive position and force Meade to attack.

Lee wouldn’t think of it.

“The enemy is there, and I am going to attack him there,” Lee said.

Longstreet obeyed orders, but he took his time organizing his men to attack the Union left. For decades thereafter, Lee’s defenders blamed Longstreet for tarrying and letting the Union army strengthen its line. The fighting on the second day — at the Peach Orchard, the Wheat Field, Devil’s Den, and Little Round Top — was some of the most furious of the war.

Late in the day, Union Gen. Winfield Scott Hancock realized that the center of his line on Cemetery Ridge was about to be overrun by Alabamians. Short of options, he ordered the 1st Minnesota, some 262 men, to charge the oncoming Confederates. More than four out of five of the Minnesotans were killed or wounded in the charge, but it was a tactical success, halting the rebels until the Union line could be reinforced.

On the Union left, rebels moved toward Little Round Top. A Union brigade, outnumbered, fought off repeated waves of rebels. Among the heroes of the battle were the men of the 20th Maine, led by a Bowdoin College professor, Col. Joshua Lawrence Chamberlain. When Chamberlain saw that his men had nearly run out of ammunition, he ordered them to fix bayonets. The Maine men charged the surprised rebels, many of whom surrendered on the spot. Thus, the Union held on to Little Round Top, which would factor into the final day of battle.

The third day

Lee had pounded the Union left and right on the first two days. On the third day, he decided to strike the Union center. His battle plan called for a charge against the center, under Longstreet’s command, plus another attack on the Union right by Ewell’s corps and an attack on the Union rear by rebel cavalry. If numbers were not in his favor, he could count on Southern ferocity and valor.

Longstreet thought otherwise. Years later, in a memoir, he wrote: “[Lee] knew that I did not believe that success was possible; that care and time should be taken to give the troops the benefit of positions and the grounds; and he should have put an officer in charge who had more confidence in his plan.”

At the point of the spear would be a division led by the dashing Gen. George Pickett. When Pickett asked, “General, shall I advance?” the despondent Longstreet couldn’t speak. He could only nod his head.

At 3 p.m. the charge began. The men did not run. They marched, in a line roughly a mile long, almost as if performing a parade drill. At first, the Union soldiers held their fire.

Then the guns opened up — first the cannons, then the muskets. From Little Round Top came an enfilading fire. Perhaps in an earlier age such an advance could have succeeded, but the weapons of the Civil War were more accurate and devastating, and the rebels were shredded. Some units reached the crest of Cemetery Ridge and briefly pierced the Union line — the so-called High-Water Mark of the Confederacy — but the federals proved too strong. Of 13,000 men who charged that ridge, half were killed, wounded or captured. All of Pickett’s 15 regimental commanders were killed or wounded, as were all three of his brigadier generals. When Pickett returned to the Confederate line, Lee told him to organize his division.

“General Lee, I have no division now,” Pickett said. Later in life, he would say bitterly that his division had been destroyed by Lee.

“It was all my fault,” Lee said as his men stumbled back to the rebel line.

That night, he was heard to say, “Too bad! Too bad! Oh, too bad!”

And the skies opened, a torrential rain that washed the blood into the soil.

The aftermath

With a third of his army killed, wounded or captured, Lee ordered a retreat. The wagon train of exhausted soldiers and wounded men stretched for 17 miles while the Potomac swelled with the summer monsoon.

News of the Union victory thrilled Lincoln, who had spent days hovering in the telegraph office, following the bulletins. But the president was astonished when, days later, he realized that Meade had not yet gone on the attack against the weakened and fleeing enemy trapped by the high water of the Potomac.

After Lee managed to slip his army across the river to the safety of Virginia, Lincoln wrote a furious letter to Meade:

“I do not believe you appreciate the magnitude of the misfortune involved in Lee’s escape. He was within your easy grasp, and to have closed upon him would, in connection with our other late successes, have ended the war.” Lincoln decided not to send the letter.

Soon thereafter, Lee tried to resign in a letter to Confederate President Jefferson Davis.

“I am becoming more and more incapable of exertion, and am thus prevented from making the personal examinations and giving the personal supervision to the operations in the field which I feel to be necessary,” Lee wrote. “I am so dull in making use of the eyes of others I am frequently misled.”

Davis, of course, refused to accept the resignation. The war ground on for nearly two years.

Could the battle have played out differently? What if Stuart had not gone astray, rendering Lee blind? What if Ewell had pushed forward to take Cemetery Hill on the first day? What if Longstreet had been quicker to attack on the second day? What if Lee had listened to Longstreet’s advice to find a more favorable place to fight? What if Meade had pursued Lee more aggressively after Gettysburg?

Such scenarios remain conjectural. And even many of the basic facts of Gettysburg remain subjects of debate and revisionism. A century and a half later it’s hard to say, with great confidence, exactly what happened, when, and why. This remains contested ground.

History isn’t the thing itself, but rather a story we tell, and the story changes, new elements are added, others forgotten, myths invented, causes imagined, facts debunked. History is a process of imposing order on a chaotic process, inventing causality and finding meaning in something that others might argue was senseless.

The consecration

The effort to consecrate this battlefield is a story unto itself, a shadow narrative. There are layers of memory here. Private citizens began trying to preserve portions of the battlefield as early as 1864.

Veterans of Union regiments showed up on anniversaries in later years to place monuments. The federal government decreed Gettysburg a national battlefield in 1895, under the War Department, which placed markers describing the actions of individual units.

Gradually, more Confederate monuments, markers and statues joined the mix. And veterans of both sides came for the big anniversaries. In 1938, about 1,800 veterans of the battle, most in their 90s, came to where they had fought 75 years earlier. Former enemies clasped hands and pledged allegiance to the same flag.

“In great deeds, something abides. On great fields something stays,” Chamberlain said in 1886 at the dedication of the monument to the 20th Maine. “Forms change and pass; bodies disappear, but spirits linger, to consecrate the ground for the vision-place of souls.”

The Gettysburg gift shop at the Visitor Center has hundreds of books for sale, dealing with the battle and the war generally, but up front, right where you walk in, is Michael Shaara’s “The Killer Angels,” the book that more than any other has shaped the way many people view Gettysburg.

The novel, published in 1974, won the Pulitzer Prize. Shaara’s masterpiece — which inspired Ken Burns to make his acclaimed Civil War documentary and then served as the basis for the movie “Gettysburg” — helped rehabilitate Longstreet’s reputation and made Chamberlain one of the superstars of the battle.

Shaara had the wisdom to understand that the quiet moments are as important as the violent ones, that much of warfare involves waiting — and not knowing what’s happening next or who exactly those soldiers are in the distance or how many columns of infantry may be coming up behind them.

Today you can walk the battlefield with your GPS-equipped smartphone, with an app that tells you exactly what happened in the place you’re standing.

The government has managed over the years to expand the boundaries of the park and restore much of it to the way it used to look. Gone is the Home Sweet Home motel, and the Stuckey’s restaurant and the privately owned observation tower. The Park Service is replanting orchards where they were during the battle. The goal is to make the battlefield like it was.

And yet a Civil War battlefield is always going to be fundamentally different in the modern era. Gettysburg today is breathtakingly serene. Plus there are informational signs and restrooms and parking lots and a museum and a gift shop.

“But, in a larger sense, we can not dedicate — we can not consecrate — we can not hallow — this ground,” the great man said that November, dedicating the national cemetery. “The brave men, living and dead, who struggled here, have consecrated it, far above our poor power to add or detract.”

Lincoln was onto something. There are moments in history that cannot be packaged in a container of words. The words fail us. All we can do is stand there, in awe. And think: This was the place. These were the rocks. This was the view. And the rest — the smoke and dust, the chaos and noise, the violence and the gore — we struggle mightily to imagine.