Travel back with us to the chilly autumn morning of November 11, 1921 — 100 years ago.

A solemn procession makes its way through the streets of Washington, from the U.S. Capitol, past the White House and across the Potomac River to the national cemetery in Arlington, Virginia. There, officials await a horse-drawn cart bearing a coffin. Inside the coffin is the body of . . . well, no one knows.

And that is the point. For on this brisk November day, three years after the end of World War I, the United States is honoring all of its unidentified war dead by paying special tribute to one of them, a randomly chosen soldier whose body was brought home from France two days earlier.

Though his identity is unknown, the public calls him Buddy, an all-American nickname that seems to comfort the families whose sons, husbands and brothers marched off to war and vanished.

“My boy did not come back,” said a sobbing woman the day before, as she stood in line for hours at the Capitol. The unknown soldier lay in state, his coffin resting on the wooden stand made in 1865 for President Abraham Lincoln’s casket. The soldier’s Capitol viewing lasted more than 16 hours. Afterward, 14 trucks were needed to transport the overflow of flowers, from kings and commoners, to Arlington National Cemetery.

This morning, the Marine Band plays Frédéric Chopin’s Funeral March as the casket is taken from the Capitol. Leading the line of mourners are President Warren G. Harding and General John J. Pershing, who commanded United States forces on the Western Front during the war. Out of respect, Pershing walks the five-mile route to the gravesite, shushing bystanders who applaud when they see him.

One year earlier, France and Great Britain, America’s allies in the war, each buried an unidentified soldier. Americans wanted their own Tomb of the Unknown Soldier.

Four unidentified U.S. military members buried in France were considered. After a random final selection, officials prepared to bring that soldier home. Meanwhile, a grave was readied on a hilltop at Arlington near the recently completed Memorial Amphitheater.

Now, on this historic day, crowds throng the site. The nation observes two minutes of silence; then bells toll. At Arlington, speeches and more wreaths follow. Harding places the Medal of Honor, the nation’s highest military award, on the casket. Other nations do likewise. As a final gesture, a Crow tribal chief removes his feather war bonnet and leaves it, a sign of respect from one warrior to another. (The headdress is displayed at the cemetery today.)

Finally, the casket is lowered into the crypt onto a bed of soil from France.

A simple stone slab covers the tomb at first. It will be a decade before a permanent replacement — a large rectangular box of gleaming white marble — is put in place. On its east side are three Greek figures representing Peace, Victory and Valor. On its west side, where Army tomb guards keep watch 24 hours a day, is this inscription: “Here rests in honored glory an American soldier known but to God.”

Although World War I is called “the war to end all wars,” it isn’t. In the decades to come, unknowns from World War II and wars in Korea and Vietnam are added at the tomb, in three crypts a few steps away from their World War I comrade.

In 1998, the Vietnam unknown is identified. He is Air Force Lieutenant Michael Blassie, whose plane was shot down in 1972. Blassie’s family wants to bury him at home in Missouri, so his now-empty crypt at Arlington is rededicated to honor all missing service members from that war.

Scientists say that improved DNA testing makes it highly unlikely that, a century after America first officially honored its wartime unknown, there will ever be another one.

Five facts

● A stone tomb is called a sarcophagus (pronounced sar-COFF-uh-gus). Egyptians carved the first stone tombs more than 4,000 years ago. They were usually displayed above ground.

● Arlington’s sarcophagus, completed in 1932 at a cost of $48,000, consists of seven pieces of Colorado Yule marble. The main section was cut in 1931 from a 56-ton block that at the time was the largest single piece of marble ever quarried in this country. The finished tomb weighs 79 tons.

● The World War I unknown soldier is buried under the sarcophagus, not inside it.

● Over the years, cracks have developed along the tomb’s exterior. Repair attempts have been mixed. Some people would like to replace the sarcophagus. Others want to retain the history of the one that is there.

● The U.S. Army has guarded the Tomb of the Unknown Soldier, also known as the Tomb of the Unknowns, since 1926. The guard was only during daylight at first, but in 1937 the duty became around-the-clock. The 3rd U.S. Infantry Regiment, known as the Old Guard, took over the watch in 1948 and is still there.

Show and tell me more

● Participate (if you live in or near the nation’s capital): A public flower-laying is set for Tuesday and Wednesday, 9 a.m. to 4 p.m. On Thursday, a full-honors procession and military flyover are scheduled, starting at 9 a.m. The public may view this free event from areas along Memorial and Eisenhower avenues, but must be in place by 8:45 a.m. All cemetery visitors need a government- or school-issued photo ID. More information is at www.army.mil/tomb.

● Watch a 23-minute movie of the Unknown Soldier’s return from France and burial at Arlington in 1921: wapo.st/3mPjKrP.

● View the exhibits in the memorial’s display room: wapo.st/2ZYQfL1.

● Learn more at the cemetery’s education website (for teachers and older students): education.arlingtoncemetery.mil/Themes/Tomb-of-the-Unknown-Soldier.

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