Execution of the thirty-eight Sioux Indians at Mankato Minnesota in December 1862. (Library of Congress Prints and Photographs Division/LIBRARY OF CONGRESS PRINTS AND PHOTOGRAPHS DIVISION)

Settlers had come from miles around. The hotels were full. And some spectators were camped out in tents and wagons.

The giant gallows erected between Front Street and the Minnesota River was a marvel: a perfect square, supported by oak timbers, and able to hold 40 nooses — 10 on each side.

It was the day after Christmas, 1862 — 150 years ago this Wednesday — and the largest mass execution in American history was scheduled for 10 a.m. in the hamlet of Mankato.

The condemned were 38 Dakota Indians convicted in what is said to be the largest killing of whites in any Indian war in American history.

There had been a delay of a week, because the authorities couldn’t find enough strong rope.

"38 Nooses" by Scott W. Berg. (Pantheon Books/PANTHEON BOOKS)

Now the Indians had painted their faces and, chanting their death songs, were guided to the gallows. They were hooded. Nooses were placed around their necks, and after three solemn beats of a drum, the platform on which they stood dropped.

Forgotten savagery

Growing up in a rambler outside St. Paul, author Scott W. Berg had always heard the story of the hanging and the savage “Dakota War” from which it grew. But he had not learned about it in school.

“We were never taught this,” he says. “But I probably heard about it when I was 7 or 10. I’m sure I heard about it by the time I was out of elementary school.”

The episode, which happened against the huge backdrop of the Civil War, is scarcely known outside Minnesota, says Berg, 46, an assistant professor of English at George Mason University.

His new book, “38 Nooses: Lincoln, Little Crow, and the Beginning of the Frontier’s End,” published by Pantheon Books, aims to end its obscurity and put it into the mainstream of its times.

Berg is also the author of the 2007 book “Grand Avenues: The Story of Pierre Charles L’Enfant, the French Visionary Who Designed Washington, D.C.

The execution’s sesquicentennial, which will be commemorated in Minnesota this week, coincides with the Civil War’s 150th anniversary. But it is part of the Indians’ tragic “parallel history,” Berg says.

He recounts the five months of killing and betrayal that raged across the prairie of southwestern Minnesota in the summer and fall of 1862, concurrent with some of the biggest battles of the sectional conflict.

Between 400 and 600 settlers — many of them women and children — were slain, along with scores of soldiers. Fewer than a hundred Indians died, Berg says, but many more would perish later of malnutrition and disease.

Coming amid the Civil War, with its lingering codes of honor and gallantry, the Dakota War was a bitter racial conflict with atrocities and talk of extermination and removal. Scalps were taken on both sides.

“They are to be treated as maniacs or wild beasts,” one U.S. Army general wrote of the Indians, “and by no means as people with whom treaties or compromises can be made.”

A newspaper editor wrote that a Dakota “has just as much right to life as a hyena, and he who would spare them is an enemy to his race.”

Far removed from the theater of the Civil War, Berg’s story still features many of its figures: Abraham Lincoln, who stayed the executions of more than 200 of the Indians, has a major role, as does disgraced Union Gen. John Pope.

Lincoln’s personal secretary, John Nicolay, and other prominent but flawed, Union generals, Henry W. Halleck and George B. McClellan appear.

New England writer Henry David Thoreau makes a brief appearance as a visitor to the area the year before the Indian war erupted.

The Indians are headed by a chieftain named Little Crow, a complicated and charismatic figure who begins the conflict with hundreds of warriors, and dies as a fugitive, accompanied only by his teenaged son.

Little Crow was scalped and his body buried in a pit used for the bones of cattle, Berg writes. It was later dug up. His head was cut off, and his skull wound up in the hands of a collector.

“It’s not a pretty picture at all,” Berg says. But it’s part of the centuries-old saga of encounters between Indians and whites, and “is part of the origin story of the country.”

It’s not “a side story,” he says. “It’s one of the two or three most important . . . stories . . . of America.”

Racism and retribution

It began with an incident over hen’s eggs in August of 1862, but its roots went back years, Berg writes.

The eggs were discovered on a farm near Acton, Minn., by four Dakota returning from a failed hunting trip.

“Sharing whiskey on the road,” Berg writes, they had intended to ask for food and drink for their journey home. They found the eggs, and apparently argued over whether to steal them.

Then they argued over which of them had the courage to shoot a white man. In the end, three white men, one woman and a 15-year-old girl were slain.

The Indians fled toward home, gathering a large entourage of sympathetic Dakotas on the way, until they reached the village of Little Crow, southwest of what is now Minneapolis/St. Paul.

Little Crow was a 52-year-old elder — a statesman, trader, healer and negotiator who had twice been to Washington, D.C.

The assembled Indians were fed up with whites, Berg writes, and had classic grievances that were deep and long-standing. They had been cheated out of their lands and their way of life. They were rarely paid the annuity promised by government treaties without some delay or string attached. They were treated poorly by racist and unscrupulous white merchants and government agents.

A band of militants among them wanted war and sought Little Crow’s approval.

Berg writes that Little Crow told the militants that they were foolish, that the whites would destroy them — but knowing that, he would still lead them in battle.

What followed was weeks of ragged warfare, with Indians attacking settlers, traders and soldiers, and soldiers counterattacking and routing the Indians.

As the Civil War’s battles of Second Bull Run and Antietam raged 1,000 miles to the east, the prairie of southwestern Minnesota filled with terror, brutality and fleeing refugees.

Among the first killed was an especially heartless trader, Andrew Myrick, who had told starving Indians they could eat grass or feces. He was found with several gunshot wounds, multiple arrows sticking out of his body and a clump of grass stuffed in his mouth.

Elsewhere, an Indian named Cut Nose used his war club to bludgeon to death at least 12 people.

In the settlement of Milford, Indians massacred the entire white population, mutilating many of the bodies. Women and children were not spared. Berg, in an interview in his campus office, noted that among the Dakota, women and children were considered combatants. They “were expected to fight, especially if the conflict spilled into a village,” he said.

The Indians went on to attack a makeshift army installation called Fort Ridgely and were twice beaten back with the help of artillery.

By Civil War standards, the numbers engaged were small. The Indians had around 800 warriors, about the size of large Union army regiment. And only only three whites and two Indians were killed.

The Indians next turned on the German immigrant village of New Ulm, which occupied a traditional Dakota camp and burial site the Indians believed was theirs.

The Dakota attacked the town’s 350 defenders in house-to-house fighting on Aug. 23. The battle was a draw, with six Indians and 14 whites killed.

Both sides retreated, and Little Crow realized it was time for a general disengagement.

Washington steps in

Meanwhile, appeals had been sent to Washington. The government sent embittered Union Gen. John Pope, who had just lost the Second Battle of Bull Run, to Minnesota to deal with the Indians.

He proceeded to bombard Washington with exaggerated tales of calamity and requests for huge numbers of reinforcements. All the requests were denied, Berg writes.

A more reliable man on the ground was one of Lincoln’s trusted personal secretaries, John G. Nicolay. He was there, coincidentally, as part of a delegation to a different Indian tribe.

He and his delegation telegraphed Lincoln: “The massacre of innocent white settlers has been fearful. A wild panic prevails.” Nicolay added in a telegram to Secretary of War Edwin M. Stanton that with the Dakota, “it must be a war of extermination.”

Out on the prairie, Little Crow’s band was in retreat, in a column of men, women, children and animals that was five miles long and a mile wide.

But there were murmers among the Indians that Little Crow had brought down the wrath of the white man on all Dakota, even those who were not militant.

Near the end of September, a force of 2,000 soldiers caught up with Little Crow’s 700 warriors, only about 300 of which were reliable fighters, Berg writes.

In the ensuing Battle of Wood Lake, the last major fight of the Dakota War, the Indians were defeated. They were broken by a bayonet charge and crippled by desertions. Fourteen soldiers were killed and mutilated. Twenty Indians were slain and then scalped in retribution, Berg writes.

Little Crow fled north with some loyalists. The others stayed behind to surrender. It was the start of the Dakota diaspora, Berg writes, and for some, the trip to the gallows.

The hangman and the hunted

With mobs of armed settlers crying for vengeance, the government began to sift through the hundreds of Indian prisoners to see who deserved punishment. A total of 392 were selected for trial.

And after legal proceedings, many of which lasted 10 minutes, 303 death sentences were meted out for fighting in battle as well as for participation in massacres.

The names of the condemned were forwarded to Lincoln, who had ordered that the record of the proceedings be sent to him for review.

He then had a special military commission go over every case.The commission whittled down the number of death sentences to 39 — for Dakota who had murdered settlers, as opposed to those who had only fought in battle. One more was spared later.

Berg quotes Lincoln as saying of execution: “If a man had more than one life, I think a little hanging might not hurt this one. But after he is once dead we cannot bring him back, no matter how sorry we may be.”

Five months later, Little Crow, now on the run and accompanied only by his son, Wowinape, paused to forage for raspberries on a farm about 50 miles west of St. Paul. Two settlers stumbled upon them ,and Little Crow was shot to death.

The date was July 3, 1863, and a thousand miles away in the parallel universe of American history, white men were slaughtering each other outside the town of Gettysburg.