The tattered map shows where the bodies of 300 Confederates were buried, row on row just outside a sunken farm lane called Hog Trough Road where they fought that day.

A few yards away, the graves of 200 Union soldiers are depicted, laid to rest where they were killed attacking the Confederates. Close by are the graves of another 240 rebels, and beside them are 40 more Union soldiers.

Almost 800 burials are shown within a small section of the sprawling field of one the most bitter battles of the American Civil War.

The 150-year-old, recently digitized map depicts the Battle of Antietam — not with the usual scenes of charge and countercharge, but as one vast cemetery.

And Civil War historians are hailing it as an important new way to visualize the toll of the huge battle outside Sharpsburg, Md., in 1862.

“Every one of us who’s looked at this absolutely flips out,” said Garry Adelman, chief historian for the Washington-based American Battlefield Trust, which works to preserve historic battlefields. “This will reverberate for decades.”

The map is the only one of its kind known to exist. It was digitized by the New York Public Library, which owns it, and was spotted online by local historians a few weeks ago.

It depicts the locations of 5,800 graves spread across a landscape of about 12 square miles.

The war was fought from 1861 to 1865 between a confederacy of Southern states that sought to maintain slavery, and Northern states and the federal government, the Union, which opposed it. The North prevailed. The country remained intact. And slavery was abolished.

Although most of the Antietam dead were moved to formal cemeteries after the war, the map was drawn up before that happened, Adelman said, perhaps in conjunction with the planned relocations.

And the grave clusters are grim new indicators of where the fighting was worst.

“It’s a visual representation of the carnage from the battle,” said Timothy H. Smith, the researcher who first stumbled on the map online. “It’s startling to look at.”

The map provides the names in some cases of the regiments or brigades to which the dead belonged. And in about 45 cases it provides the names of individual buried soldiers.

It marks the grave of Pvt. John Marshall, of the 28th Pennsylvania regiment. The burial, at the foot of a dead tree, was the subject of a famous photograph taken just after the battle. (Photo historian William A. Frassanito has identified Marshall as a 50-year-old Irish immigrant from a suburb of Pittsburgh.)

It pinpoints the grave of Lt. Col. John L. Stetson, of the 59th New York regiment, one of the outfit’s 71 men killed in the battle. His grave may have been easy to spot by early surveyors because his father, Lemuel, traveled to Sharpsburg days after the battle to mark it.

“I found the burial rude and imperfect, like all soldiers’ graves upon the field,” the elder Stetson wrote. So he and “a burial party” of soldiers improved it.

“I … had a wall twenty inches high built around the grave,” he wrote in a letter found by historian Jim Buchanan.

“This was filled with fresh earth,” Stetson wrote. “Along the sides to the crest I laid slabs of dark brown limestone, [and] at the head and foot stand heavy stones trenched into the ground. Over the whole I [laid] green boughs cut from the top of the white oaks felled by the cannon shot.”

And the map marks the grave of Nicholas Jachum, 20, who was one of the 45 men from the 9th New York infantry regiment to be killed in fighting near Antietam Creek, where he was buried.

“The air was full of the hiss of bullets and the hurtle of grape-shot,” a comrade from the 9th wrote later. “The mental strain was so great that I saw at that moment the singular effect … [where] the whole landscape for an instant turned slightly red.”

The map has some mistakes.

One Union regiment is identified as the 1st Maryland infantry regiment, which should be the 1st Minnesota, historians say.

“G. D. Berry,” of the 13th Massachusetts, buried near an area called the East Woods, is probably George O. Berry, 21, of Stoneham, Mass.

And “Geo. Dow,” of the 20th New York regiment is probably George Dorr, 23, who had enlisted in New York City three weeks after the war started.

But overall the map may be “our very earliest representation of the entire battlefield of Antietam,” Adelman said. “On a scale from one to 10 of Civil War battlefield discoveries … I’d call it a 9.5.”

The battle, a Union victory, claimed the lives of about 7,000 men, the National Park Service says. But it gave President Abraham Lincoln the opportunity, five days after the battle, to announce the Emancipation Proclamation.

That declared many, but not all, enslaved people across the United States free, as of Jan. 1, 1863, and changed the character of the war into a moral crusade for freedom, according to the National Archives, which has the original.

The battle took place on Sept. 17, 1862, around Sharpsburg, a village 70 miles northwest of Washington. Roughly 87,000 Union soldiers under Gen. George B. McClellan fought 45,000 Confederates under Gen. Robert E. Lee from dawn to dark.

The contest was a tactical draw, but Lee fled back to Virginia.

About 23,000 men from both sides were killed, wounded or missing, and the deceased were strewn across a five-mile long swath of cornfields, woods and country lanes mainly west of the creek.

Many were still there when Washington photographer Alexander Gardner arrived, a day or two after the battle. He photographed dead soldiers, graves and burial details, and his disturbing pictures sobered the public when they were displayed in New York City the next month.

The graves were still there two years later when the map was made in 1864.

They “ranged from single burials to long, shallow trenches accommodating hundreds,” according to the National Park Service. “Grave markings were somewhat haphazard, from stone piles to rough-hewn crosses and wooden headboards.”

The map is attributed to Simon G. Elliott, a California railroad surveyor of mixed repute. He probably created it when he was in Washington working as a lobbyist, said Andrew I. Dalton, director of the Adams County Historical Society, in Gettysburg, who has researched Elliott.

Elliott had done a similar map of the Gettysburg battlefield, which is well known to historians. Few people knew he had also done an Antietam map, Adelman said.

But experts at the New York Public Library did, and they included it in a project in which they scanned more than 3,000 antiquarian maps of the United States and North America. The project, funded by the National Endowment for the Humanities, ran from 2015 to 2018.

The library has had the map probably since it was first published in New York in 1864 and was well aware of its rarity and importance, Ian Fowler, a curator in the library’s map division, said in an email.

But the scanning project made it available online for the first time, he said.

That’s where Smith, the researcher, spotted it.

He had called up what he thought was Elliott’s Gettysburg map on the library’s website and realized as it downloaded that it showed Antietam.

“I was like, ‘Wait a minute, this isn’t Gettysburg,’ ” said Smith, historian and collections manager at the Adams County Historical Society.

He suspected “immediately that this is something that’s never been seen” by historians, he said. “I have not talked to anyone who had any inkling that this thing existed.”

As for Elliott, it’s not known why he produced the map, how he did it, or if he ever actually went to the battlefield.

Smith said he may have relied on surveys done by locals who were recording the grave locations for eventual moves to cemeteries and for families who came to take the bodies of loved ones home.

“He just drew the map, he is the mapmaker, he took the information that had been gathered and he made it into this visual presentation that’s very startling,” Smith said.

After the war, a formal cemetery was established, now the Antietam National Cemetery in Sharpsburg, and in 1866, the process of exhuming the remaining dead from the battlefield began. (Dead Confederates were buried in other local cemeteries.)

“The dead were identified by letters, receipts, diaries, photographs, marks on belts or cartridge boxes, and by interviewing relatives and survivors,” the Park Service says on the cemetery website.

The cemetery was dedicated on Sept. 17, 1867. More than 4,500 Union soldiers killed at Antietam and other battles in Maryland are buried there.

Eighteen hundred of them have never been identified.

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