Arlington National Cemetery had never seen a funeral quite like the one that was held the morning of Nov. 11, 1921. The nation’s highest military officers were there, along with congressional leaders, Supreme Court justices, diplomats from around the world and a crowd so huge the president’s car was forced to drive across fields for him to get there in time.

An “homage of a hundred million” was how one breathless headline writer described the unprecedented turnout and a funeral that took up nearly the entire front page of the next day’s Washington Post.

It was a historic honor for one person, although no one in attendance knew who that person was.

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Today, the Tomb of the Unknown Soldier is as solid in the public psyche as its massive marble slabs are heavy on that hallowed ground. The resting place of one “soldier known but to God” sits at the center of national remembrance, drawing millions of visitors a year and an annual pilgrimage from the commander in chief.

Before that autumn morning, there had been no such tradition. Monuments to the unnamed dead had always been collective. The original site of Memorial Day ceremonies at Arlington was an enormous ossuary containing bones from 2,111 soldiers gathered from Civil War battlefields.

But the killing technologies of World War I brought new levels of identity-wiping devastation. More than 116,000 Americans were slaughtered, including 1,652 who were too damaged to be identified.

“People could be atomized by a shell fired from five miles away,” said Philip Bigler, the former of historian at Arlington National Cemetery and author of a soon-to-be-released book, “Tomb of the Unknown Soldier: A Century of Honor.”

Britain, which suffered even greater losses, didn’t allow its dead to be brought home for burial to avoid years of disheartening and politically destabilizing funerals.

Instead, on Nov. 11, 1920, the second anniversary of the armistice that ended the war, the British military buried an unknown casualty at Westminster Abbey with state honors. France, likewise, interred an unknown soldier at the Arc de Triomphe.

In Washington, decorated World War I veteran and Rep. Hamilton Fish (R-N.Y.) proposed the United States do the same. New York City offered to host the memorial in its new Pershing Square. Some lawmakers wanted to put the body in the crypt beneath the Capitol Rotunda that had been designed for — and refused by — George Washington. But in March 1921, Congress approved a measure to locate the tomb in front of the newly constructed Memorial Amphitheater at Arlington.

For Fish, the white officer who led the African American Harlem Hellfighters in combat, the key was to honor a soldier who could have been of any rank or race. “The whole purpose of this resolution is to bring home the body of an unknown American warrior who in himself represents no section, creed, or race,” Fish said in congressional testimony, “who typified, more­over, the soul of America and the supreme sacrifice of her heroic dead.”

As work started on the tomb, officers in Europe began the tricky work of finding a suitably unidentified body to fill it.

It took tremendous efforts to keep the Unknown Soldier from being known, even just a little bit. Officials didn’t want anyone to suss out even where the soldier had been killed — be it Belleau Wood, Marne or Meuse-Argonne — so he could better represent every casualty.

To start, they disinterred four sets of remains from American battlefield cemeteries in France and made doubly sure there was no way to get a trace on their identities, no scrap of a letter, rosary or distinguishing mark.

On Oct. 23, they arrived at the village of Chalons-sur-Marne. In a specially decorated room in the city hall, the unmarked coffins were placed on their shipping crates, which had been draped with American flags to conceal any hint of which cemetery they had come from. A combined French and American honor guard stood post.

Early the next morning, an American major shuffled the coffins again, putting them on crates other than their own. With a crowd of onlookers outside, a military band in the courtyard and senior officers lining the corridor, a much-decorated American enlisted man, Sgt. Edward F. Younger, entered the chamber carrying a spray of white roses. After circling the four caskets more than once, Younger placed the roses on one, stepped back, and saluted it.

That morning, the Unknown Soldier began an unprecedented ceremonial journey from Northeastern France to a bluff over the Potomac River. (The three unselected bodies were buried not far from Paris.)

The casket, still carrying its spray of roses, was rolled through town on a caisson, escorted by Army units from both countries, generals, military bands, Boy Scouts and American Legionnaires. Local widows, many in black, lined the route to the railroad station.

An honor guard stayed with the casket day and night during its rail journey to Paris and then to the port of Le Havre, where more crowds, speeches and salutes awaited.

Schoolchildren threw flower petals as they proceeded to the docks. Six sailors and two Marines took possession of the casket from the Army body bearers and carried it to a place of honor at the stern of the USS Olympia. A 17-gun salute boomed around the port as the cruiser and its escorting destroyer put to sea, followed at the start by eight French naval vessels.

“The French very much appreciated the United States coming over there,” Bigler said. “There was a sense that this had been an American victory.”

Two weeks later, the Olympia docked at the Washington Navy Yard and the pomp continued. The ship was greeted by the the Marine commandant, the secretary of the Navy and Gen. John J. Pershing.

Following an enormous and meticulously timed procession to the Capitol, the Unknown Soldier lay in state in the Rotunda, his casket resting on the platform, or catafalque, built for Abraham Lincoln. Among the first to pay respects were President Warren G. Harding. His wife, Florence, placed a ribbon next to the spray of roses. More than 90,000 people passed through on Nov. 10.

The next day — Armistice Day (now called Veterans Day) — the walking parade from the Capitol to Arlington was a “Procession Without Parallel,” according to the next day’s Post.

The soldier’s caisson was accompanied by the president, chief justice, Pershing and the chiefs of staff, members of Congress, more than 40 fraternal groups and Medal of Honor winners marching four abreast. Only former president Woodrow Wilson, who had suffered a stroke, rode in a carriage.

“All America, Rich and Poor, Aged and Young, President and Commoner, Solemnly Bares Head to Unknown Hero,” read a headline.

More than 5,000 tickets had been distributed, swamping the capacity of the amphitheater. Fish laid a wreath, as did Chief Plenty Coups, leader of the Crow Nation. Following the ceremonies, the soldier was lowered onto a layer of soil from France and a three-volley salute fired.

It would be a decade before the budget process allowed the simple slab to be replaced with the sculpted Colorado marble tomb that is there today, its sunset-facing side bearing the familiar epitaph: “HERE RESTS IN HONORED GLORY AN AMERICAN SOLDIER KNOWN BUT TO GOD.”

Nearly a century later, countless flowers and wreaths have been placed before the tomb (and the unknown fallen from World War II and Korea that came in later years), laid by presidents and veterans and the simply grateful. Within the stone, beneath the dust of ancient white roses, rests a nameless soldier known around the world.

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