A spine of gray limestone runs north and south through the legendary cornfield here, just breaking the surface and leaving a path where no corn can grow.

For a century and a half, the elements have scoured the dirt, and crops have come and gone. But the stone has remained, scarred and smoothed by the plow and the weather.

On the morning of Sept. 17, 1862, the feet of thousands of desperate soldiers hurried across the ancient rock. Some men fell and bled on it. Bullets and shells flew over it. And somewhere nearby toppled the Lone Star flag of the 1st Texas Infantry Regiment.

In this stony cornfield, the doomed 1st Texas lost, along with its flag, 82 percent of its men. Here, the Civil War’s Battle of Antietam exploded in fury, and here, a crucial, bloody step was taken toward the end of slavery in America.

“Of all the days on all the fields where American soldiers have fought, the most terrible by almost any measure” was here at Antietam, historian Stephen W. Sears wrote in his classic 1983 study of the battle.

Read the full Washington Post Civil War 150 series.

In the late summer and fall of 1862, as the Civil War moved through its second year, it had reached frightful new levels of violence, which would grow as the war went on.

But the fight along Antietam Creek, 150 years ago this month, would endure as its bloodiest single-day battle, and its horrors would haunt the soldiers who fought there for years.

Packed into 12 hours of conflict that began under the stars before dawn and that ended around sunset were three different phases — morning, midday and afternoon — and more than five different sub-battles.

Six generals were killed, three on each side. Almost 4,000 men were killed outright and 17,000 more were wounded. Of those, thousands would succumb to their injuries in the following months. Still more were reported missing.

There was at least one suicide, one Union officer who fled from his command in terror, and one dog slain beside its dead master, a Union officer.

A Union regiment, the 15th Massachusetts, lost many of its 606 men to friendly fire.

The more than 23,000 killed, wounded and missing from both sides “were the highest casualties of any one-day battle in our entire nation’s history,” said historian Tom Clemens, a retired professor at Hagerstown Community College and a student of the battle.

About three times as many Americans were casualties outside Sharpsburg as were killed or wounded in the landings in Normandy on D-Day in 1944.

The battle of Antietam, (pronounced an-TEE-tam) took place about 19 miles west of Frederick, just north of where the creek flows into the Potomac River, 54 miles northwest of Washington.

The clash pitted Gen. George B. McClellan’s roughly 86,000-man Union army against Gen. Robert E. Lee’s roughly 40,000 Confederates.

It is considered by many historians to be a tactical draw but a vital, strategic victory for the North.

The battered rebels were forced to retreat back across the Potomac, ending a string of triumphs and their first major incursion into Union territory in the East.

President Abraham Lincoln seized on Antietam to issue his preliminary Emancipation Proclamation, which declared millions of slaves in the South free and elevated the war to a new moral plane.

And the victory probably denied the Confederacy coveted recognition by European countries who were on the verge of such action.

It was “a game changer,” Clemens said.

For the soldiers who fought there, Antietam was a nightmarish struggle that made such place names as “the cornfield,” “the Sunken Road,” “the Dunker church” and “the Burnside bridge” infamous.

The roller-coaster terrain, with dips and hills and patches of woods and cultivated fields, resulted in opposing soldiers colliding at extremely close range, with deadly consequences.

In one part of the battlefield, the tide of fighting swept back and forth — across the turnpike to Hagerstown, around the tiny whitewashed Dunker church and in the trampled scrabble of the cornfield.

Washington photographer Alexander Gardner, who was there two days after the fighting, took grisly pictures of a line of dead Louisiana soldiers in rigor mortis strewn along the turnpike fence. He photographed the bodies of others gathered near the Dunker church, and still others scattered around a rocky outcrop near the 30-acre cornfield.

Elsewhere, the contest was more stubborn. South of the cornfield, rebels hunkered in a sunken lane called Hog Trough Road and blasted away at waves of Yankees who came over a ridge 50 yards away. The Federals blasted back.

Gardner captured the aftermath of that, too — the road, forever after called Bloody Lane, littered with what one Union soldier called a “ghastly flooring” of the dead.

And then southeast of town, in some of the battle’s later phases, Union soldiers spent much of the day trying to cross the placid creek in the face of Confederates who were hidden on a bluff across the creek and shot them down in midstream.

“Antietam stands among the foremost of all Civil War battles for the intensity of its combat,” said historian James M. McPherson, author of a 2002 study of the campaign, “Crossroads of Freedom.”

“Soldiers who experienced several battles — Antietam, Gettysburg and many others in the eastern theater — often looked back upon Antietam as by far the most horrible,” he said.

Sears, the historian, quoted a diarist from the 9th Pennsylvania, who wrote, “No tongue can tell, no mind conceive, no pen portray the . . . sights I witnessed.”

Oliver Wendell Holmes, who went to the battlefield while searching for his wounded son, remembered: “It was like the table of some hideous orgy left uncleared, and one turned away disgusted from its broken fragments.”

And years later, Rufus R. Dawes, who had been a 24-year-old major with the 6th Wisconsin, reflected on all the battles he had witnessed:

“The ‘angle of death’ at Spotsylvania . . . the Cold Harbor ‘slaughter pen’ . . . the Fredericksburg Stone Wall . . . were all mentally compared by me,” he wrote. But the scene at Antietam’s Hagerstown Turnpike “surpassed all in manifest evidence of slaughter.”

A stumbling start

It had drizzled the night before, and the two sides had jousted in the dark until they wound up facing each other on Sept. 17 along a zig-zag, four-mile front that ran north and south parallel to the creek.

Lee, the Confederate commander, had decided to invade Maryland after his rout of a befuddled Union army at the Second Battle of Bull Run two weeks before.

Aware of upcoming elections in the North and the prospect of European recognition of the Confederacy, Lee believed the South could demonstrate its power and demand its independence, McPherson wrote in his book.

Lee also expected a warm welcome in Maryland, a slave state that had not seceded, and proclaimed that the Confederates would help throw off the “foreign yoke.”

But his enterprise stumbled from the start. He wrote later that thousands of his men — some from exhaustion, some from “unworthy motives” — absented themselves.

As a result, he recounted, his invading army consisted of fewer than 40,000 worn-out soldiers.

In addition, the ragged Confederates were greeted coldly by local Marylanders, who had few slaves and a strong loyalty to the Union.

“Dirty, lank, ugly specimens of humanity,” a woman in Frederick wrote of them. “Shocks of hair sticking through the holes in their hats, and the dust thick on their dirty faces.”

Finally, Lee fell prey to one of the biggest intelligence blunders of the war. Days before the battle, a copy of his marching orders — wrapped around three cigars — was discovered in a field by an alert Yankee corporal.

Upon receipt of Lee’s orders, McClellan, the Union commander, reportedly exulted: “Now I know what to do!”

But in the end, most historians agree, the hapless “Little Mac” didn’t know what to do. [For a contrary view, see Page Q10.]

Carnage in the corn

The battle opened around dawn with a series of back-and-forth thrusts on the northern end of the field, as the sides fought over woodlots, the Dunker church — named for its full-immersion Baptist congregants — and the cornfield.

The corn in those days was far more scraggly than the lush crop that grows there today, notes the National Park Service's chief Antietam historian, Ted Alexander. This made for less cover and deadlier shooting.

One Union commander wrote later that most of the stalks were cut so close to the ground that it looked as though they had been chopped down with a knife.

“The bullets began to clip through the corn, and spin through the soft furrows — thick, almost, as hail,” recalled Maj. Dawes, whose regiment chased the rebels into the field.

“Shells burst around us, the fragments tearing up the ground, and the canister whistled through the corn above us,” he wrote.

“Our lines on the left now came sweeping forward,” he recalled. “I ordered my men to join in the advance, and commanded: ‘Forward — guide left — march!’ ”

He could see the little church of the pacifist Dunkers in the distance, but as the Yankees approached, a long line of rebels who had taken cover on the ground jumped up and fired.

“Men, I can not say fell; they were knocked out of the ranks by dozens,” Dawes recalled.

Then the Confederates counterattacked. The depleted Federals fled — “back to the corn, and back through the corn,” Dawes remembered.

As they ran, they left behind the fallen commander of the regiment’s F Company, Capt. Werner Von Bachelle, a former officer in the French army.

Von Bachelle’s Newfoundland dog would not leave his body, though, and two days after the battle the dog was found dead atop the captain, Dawes wrote. “We buried him with his master.”

Lone Star loss

Now it was the rebels plunging into the shredded corn, with a brigade made up mostly of regiments from Texas — the “Ragged Old First,” carrying a red, white and blue Lone Star regimental flag.

“I entered a corn-field and soon became engaged with a force of the enemy, driving them before me to the farther side,” Lt. Col. Philip A. Work, commander of the 1st Texas, reported after the battle.

“As soon as the regiment became engaged . . . in the corn-field, it became impossible to restrain the men, and they rushed forward,” he recounted. But they quickly got too far ahead and became isolated.

Work was unable to slow his men until they had reached the far side of the field and became exposed to intense Yankee gunfire from his flank and rear.

Work realized his precarious position, and with only a “handful of men” left, he ordered retreat.

As they did, the regimental flag bearer was hit. Another man grabbed the banner, but he, too, went down. In the chaos, no one noticed. Work reported that when they emerged from the corn, he realized they’d lost the flag.

No one knew where it had fallen. The corn was dense enough that no one could spot the banner. And a Federal counterattack was closing in.

“I entered the engagement with 226 men, [and] officers . . . of which . . . 170 are known to have been killed and wounded,” he reported. Twelve others were missing “and, doubtless, also killed or wounded.”

The 1st Texas, historians say, sustained at Antietam one of the the highest casualty rates of any regiment on either side on a single day during the war.

Company F was wiped out, historian Jerry W. Holsworth wrote in a 1996 study of the Texans in Blue & Gray magazine. Only one man was left from Company A, two from Company C and three from Company E.

“It is hard to imagine Col. Work’s feelings as he gazed at what was left of his regiment,” Holsworth wrote.

Work was further dismayed by the loss of the flag — the white star is said to have been made from the wedding dress of the wife of its first commander, the rabid secessionist Louis T. Wigfall.

“It is a source of mortification . . . that . . . our colors were not brought off,” Work lamented.

“Some degree of odium must attach under the most favorable circumstances,” he wrote afterward. “And although such are the circumstances surrounding the conduct of this regiment, the loss of our flag will always remain a matter of sore and deep regret.”

After the rebels retreated, Samuel Johnson, a Union private from the 9th Pennsylvania Reserves, found the Texas regimental flag, and another flag, in the cornfield, according to Holsworth.

And in an account penned 40 years later, an old rebel who had been captured in the battle heard Johnson say that 13 dead Confederates were sprawled around the lone star flag when he found it.

(In 1905, the flag was returned to Texas by President Theodore Roosevelt and today resides in the state archives building in Austin.)

Despite all the bloodshed in the cornfield, it was still only about 7:30 a.m. The thunder of the battle rolled south to the church, the Sunken Road and the bridge in what one veteran called a “carnival of death and suffering.”

In the end, the Federals seized the Sunken Road and eventually got across the bridge, only to be stymied by late-arriving rebel reinforcements.

More than 12 hours after it started, the fighting finally ceased, in a stalemate.

“As the sun sank to rest . . . the last sounds of battle along Antietam Creek died away,” Francis W. Palfrey, a historian and a wounded veteran of the battle, wrote in 1889.

“The corn and trees, so fresh and green in the morning, were reddened with blood,” he wrote. “The blessed night came, and brought with it sleep and forgetfulness . . . but the murmur of the night wind . . . was mingled with the groans of the countless sufferers of both armies.

“Who can tell?” he wondered. “Who can imagine, the horrors of such a night, while the unconscious stars shone above, and the unconscious river went rippling by?”