The Civil War began here shortly before dawn when a mortar on the starlit beach fired a single shot high into the sky over this proud and elegant city.

From Fort Sumter, the gun’s target out in the harbor, and from points ashore, people watched the shell arc overhead, the path marked by its burning fuse.

It was a fateful moment — one of the most profound in U.S. history — and in many ways the moment modern America was born.

Turn back the pages of the nation’s story, chapter by chapter, decade by decade, across the past century and a half, and you eventually get here: a place of pilgrimage today, where 700,000 people come every year to imagine what it was like.

April 12, 1861. Capt. George S. James of the South Carolina battalion of artillery, standing by his stubby gun on the beach, holding his pocket watch, waiting to open fire

In town, on Meeting Street, the bells of white-steepled St. Michael’s church strike 4 a.m. The minutes pass. At 4:30, there is the distant flash of James’s gun. A delayed boom, like a firework on the Fourth of July.

And the single shell fired by the fledgling Confederacy is lofted toward the Union garrison holed up in the brick fort. The last few seconds of the old America seem suspended for an instant before the shell explodes, changing the nation forever.

“I sprang out of bed,” wrote the diarist Mary Chesnut, who was in Charleston that night, “and on my knees . . . prayed as I never prayed before.”

From dozens of Confederate guns, shot and shell now rained on Fort Sumter, “as if an army of devils,” a soldier inside recalled later.

Few people grasped the ultimate meaning of the crisis that had just unfolded.

Some sensed it would bring war. Many did not. They still believed the South would be permitted to peacefully separate from the Union.

Only a handful realized it might mean freedom for the slaves. The abolitionist and former slave Frederick Douglass was one.

“We have no tears to shed . . . over the fall of Fort Sumter,” he wrote later. “God be praised. . . . The dealers in the bodies and souls of men . . . have exposed the throat of slavery to the keen knife of liberty.”

There was, indeed, more at stake than the “momentous issue of civil war,” as Abraham Lincoln had said in his inaugural address six weeks earlier.

Would the United States be one country or two?

How would the outcome affect history 50 years hence, a hundred years hence?

What would be the fate of the 4 million enslaved African Americans and their descendants?

Here, with townsfolk watching from rooftops, the opening act of the Civil War played out, beginning a drama that would claim the lives of 2 percent of the American population — the equivalent of 6 million people today.

The dead would include Capt. James — killed at the Battle of South Mountain, in Maryland, in 1862.

Fort Sumter is still perched on its shoal at the entrance to Charleston’s shimmering harbor as modern container ships the size of buildings glide by, headed to sea.

The city, which the late historian Bruce Catton called “the past incarnate,” feels like a polished antique jewel. In early spring, it is cooled by the ocean wind, which rustles ancient live oak trees much older than the Civil War.

On Tuesday morning, 150 years to the minute after James’s gun was fired, a somber candlelight concert is scheduled to begin in Charleston’s waterfront White Point Garden. Out in the darkened harbor, the fort will be illuminated and marked by a vertical shaft of light from inside that will split in two at 4:30 a.m.

“No fireworks, no celebration,” said Charleston lawyer Robert N. Rosen, president of the Fort Sumter-Fort Moultrie Historical Trust. “It’s probably the most tragic moment in American history.”

In Charleston, as the militant capital of slavery, secession and southernism, jubilant crowds thronged the streets that day.

“We, perhaps, may have just commenced the opening of events that may not end in our . . . generation,” Francis W. Pickens, South Carolina’s governor, said proudly from the balcony of a Charleston hotel.

Eight months later, much of the joyous city — including the hall where the secession ordinance passed — was destroyed by a wind-blown fire that left it looking like a bombed-out wasteland for the rest of the war.

In the North, the Sumter attack galvanized a divided, indifferent population for “war, vigorous war, war to the bitter end,” as Douglass put it.

Inside Sumter, its commander, Maj. Robert Anderson, 55, who had desperately sought to avoid conflict, was broken by his ordeal.

“God grant that neither I nor any other officer . . . may again be placed in a position of such mortification and humiliation,” he had written a week earlier.

It is likely that no American officer has ever been in such a political, diplomatic and military pressure cooker for so long, with so much in the balance, and so little guidance from his government.

Anderson, a native of Kentucky who was wounded during the Mexican War and detested the brutality of combat, had been ordered to take command of Union forces at Charleston five months earlier, on Nov. 15, 1860.

This was nine days after the election of Abraham Lincoln, who opposed slavery and was determined to block its extension. South Carolina, where more than half the population was enslaved, had vowed that Lincoln’s election would mean its secession from the Union.

Anderson was first sent not to Fort Sumter, which sat unfinished and unoccupied, but to a sleepy, shore-side installation called Fort Moultrie outside the city.

Moultrie had a complement of about 80 men. And when Anderson arrived Nov. 21, he realized it had gone to seed.

Fort Sumter, on the other hand, was “the key,” he wrote. Although incomplete, it had 12-foot-thick brick walls that were 50 feet high, and it sat like a blunt arrowhead pointed straight at the shipping channel into the city.

As the crisis deepened, Anderson begged Washington for reinforcements. “The clouds are threatening,” he wrote, “and the storm may break upon us at any moment.”

On Dec. 20, 1860, South Carolina delegates, meeting in Charleston, voted to secede. And the major now found himself manning an isolated outpost in a hostile country.

“If attacked in force, headed by any one not a simpleton,” he wrote a friend, there was little chance he could hold out.

But the weak lame-duck administration of President James Buchanan feared that any reinforcement might spur “a collision,” as the newspapers delicately put it.

Anderson was on his own. Menaced by the growing Confederate forces, ordered to avoid provocation, he wrote that he felt like a tethered sheep “watching the butcher” sharpen his knife.

All this time, he had been eyeing Fort Sumter. He had clearance to move his command there if attacked or if he had “tangible evidence” of a coming attack.

By Christmas, he had made his decision.

Sumter, with its 60 guns, would provide security for his command. Occupied, its strength might give the enemy pause and might even defuse the crisis, he hoped.

As night fell on Dec. 26, 1860, Anderson slipped his garrison across the channel and into Fort Sumter.

There, the next morning, after kneeling in prayer, he raised Fort Moultrie’s giant, 36-foot-long garrison flag, which he had brought with him.

Ashore, Charlestonians were enraged. They thought they had an understanding with Buchanan that no such move would be undertaken.

“We have been treacherously dealt with,” one resident wrote, according to historian David Detzer’s account of the crisis. “The die has been cast and we may now look for civil war.”

The next three months saw a steady escalation of the tension.

Anderson’s provisions dwindled as the South Carolinians ringed Sumter with weaponry and Washington fumbled.

On Jan. 9, 1861, the Star of the West, a resupply and reinforcement ship Anderson didn’t know was coming, approached the harbor and was driven off by enemy gunfire while the Sumter garrison watched, afraid of sparking hostilities.

A story is told that a Union soldier’s wife, incensed at the timidity, lunged forward to fire a gun at the rebels and was restrained by an officer. Not all historians accept the account, however.

On March 1, the newly minted Confederate general P.G.T. Beauregard, 43, a former student of Anderson’s at West Point, took command of the Charleston forces, with orders to seize Fort Sumter as soon as possible.

Three days later, in Washington, Lincoln was inaugurated, declaring secession “void” and promising to “hold, occupy and possess” all government property.

The collision seemed inevitable.

By April 3, Anderson was down to a few days’ worth of bread. He pleaded for orders: “I . . . most respectfully and urgently ask for instructions what I am to do as soon as my provisions are exhausted.”

The same day, there was suddenly more shooting from the rebel batteries. A mystery ship showing the stars and stripes was entering the harbor. The fort went on alert. Anderson again held his fire.

But it was another bungle. The ship was the Rhoda H. Shannon, a schooner bound from Boston to Savannah with a cargo of ice.

Her clueless skipper, Joseph Marts, got lost in the weather, thought Charleston was Savannah — 100 miles to the south — and sailed into the middle of the standoff, almost igniting the Civil War.

The tension in Charleston was now unbearable. “One’s heart is in one’s mouth all the time,” Chesnut wrote.

Yet the city was also giddy. One woman told Chesnut that she felt sorry for those who were not present.

On April 6, Lincoln, determined to make the Confederates back down or fire the first shot at the fort, sent a messenger to Pickens and Beauregard, saying that a relief expedition was going to Fort Sumter.

Anderson got a similar message and was urged to hold out. But, he was told, if capitulation seemed necessary, he was authorized to surrender.

In light of Lincoln’s ultimatum, the Confederate government ordered Beauregard to demand the fort’s evacuation and, if refused, “reduce” it.

On April 11, Beauregard sent to the fort a delegation headed by Chesnut’s husband, James, a former U.S. senator, to call for its surrender. Anderson declined but added that if not attacked, he would be “starved out” in a few days.

At 12:45 the next morning, April 12, the Confederates returned for a final parley. They wanted to know when, exactly, Anderson planned to leave.

The major was evasive and seemed to be stalling. At 3:20 a.m., James Chesnut, on behalf of Beauregard, informed Anderson that the Confederates would open fire in an hour. It took a little longer.

Capt. James’s shot signaled the general bombardment, which went on for 34 hours. More than 3,300 shells were fired from the ring of enemy batteries, and the fort suffered 600 direct hits.

Its flag was shot down and raised again. Its barracks caught fire. Its walls were cratered.

By 1 p.m. April 13, it was a smoking inferno, and, amid overtures from three Confederate delegations, Anderson gave up.

He and his command left the fort at 4 p.m. the next day after firing a long artillery salute. And on April 15, as a ship bore the garrison out of the harbor, rebels lined the shore, with their hats off.

Already, though, the war’s first fatality had occurred. During the artillery salute, a premature explosion had accidentally killed Union gunner Daniel Hough. He was buried somewhere on the parade ground, where he might still rest.

Today, guides tell visitors who take the sightseeing boat to Fort Sumter that the grave of Hough — the first of the war’s 620,000 fallen — has been lost.

And so has the anguish that once defined the name Sumter.

Charleston’s longtime mayor, Joseph P. Riley Jr., whose great-great-grandfather fought for the Confederacy and walked home from Virginia in 1865, said the fort has long existed at the back of the city’s mind.

Growing up, he said, you knew it was there, off in the distance, a place of tragedy and beauty.

“It was a part of our city’s history,” he said. “Rising out of our beautiful harbor . . . part of our community. You probably took it for granted. . . . You accept it as being there. It was always there.”

A few weeks before Sumter fell, Samuel Wylie Crawford, the fort’s assistant surgeon, had predicted what he believed would happen when it was assaulted.

“The first gun fired at our fort will call the country to arms,” he wrote to his brother in February. “The bugle that sounds that attack . . . will echo along the slopes of the Alleghenies amid the granite hills of the North, along the shores of the Great Lakes, and far away on the rolling prairies of the West — and the earth will shake with the tread of armed men.”