From 1914 to 1918, World War I took a greater human toll than any previous conflict, with some 8.5 million soldiers dead of battlefield injuries or disease. The Great War, as it was then known, also ravaged the landscape of Western Europe, where most of the fiercest fighting took place. From the devastated landscape of the battlefields, the red poppy would grow and, thanks to a famous poem, become a powerful symbol of remembrance.

Across northern France and Flanders (northern Belgium), the brutal clashes between Allied and Central Powers soldiers tore up fields and forests, tearing up trees and plants and wreaking havoc on the soil beneath. But in the warm early spring of 1915, bright red flowers began peeking through the battle-scarred land: Papaver rhoeas, known variously as the Flanders poppy, corn poppy, red poppy and corn rose. As Chris McNab, author of The Book of the Poppy, wrote in an excerpt published in the Independent, the brilliantly colored flower is actually classified as a weed, which makes sense given its tenacious nature.

Lieutenant Colonel John McCrae, a Canadian who served as a brigade surgeon for an Allied artillery unit, spotted a cluster of poppies that spring, shortly after the Second Battle of Ypres. McCrae tended to the wounded and got a firsthand look at the carnage of that clash, in which the Germans unleashed lethal chlorine gas for the first time in the war. Some 87,000 Allied soldiers were killed, wounded or went missing in the battle (as well as 37,000 on the German side); a friend of McCrae’s, Lieutenant Alexis Helmer, was among the dead.

Struck by the sight of bright red blooms on broken ground, McCrae wrote a poem, “In Flanders Field,” in which he channeled the voice of the fallen soldiers buried under those hardy poppies. Published in Punch magazine in late 1915, the poem would be used at countless memorial ceremonies and became one of the most famous works of art to emerge from the Great War. Its fame had spread far and wide by the time McCrae himself died, from pneumonia and meningitis, in January 1918.

Across the Atlantic, a woman named Moina Michael read “In Flanders Field” in the pages of Ladies’ Home Journal that November, just two days before the armistice. A professor at the University of Georgia at the time the war broke out, Michael had taken a leave of absence to volunteer at the New York headquarters of the Young Women’s Christian Association (YWCA), which trained and sponsored workers overseas. Inspired by McCrae’s verses, Michael wrote her own poem in response, which she called “We Shall Keep Faith.”

As a sign of this faith, and a remembrance of the sacrifices of Flanders Field, Michael vowed to always wear a red poppy; she found an initial batch of fabric blooms for herself and her colleagues at a department store. After the war ended, she returned to the university town of Athens and came up with the idea of making and selling red silk poppies to raise money to support returning veterans.

Michael’s campaign to create a national symbol for remembrance—a poppy in the colors of the Allied nations’ flags entwined around a victory torch—didn’t get very far at first. But in mid-1920, she managed to get Georgia’s branch of the American Legion, a veteran’s group, to adopt the poppy (minus the torch) as its symbol. Soon after that, the National American Legion voted to use the poppy as the official U.S. national emblem of remembrance when its members convened in Cleveland in September 1920.

On the opposite side of the Atlantic, a Frenchwoman named Anna Guérin had championed the symbolic power of the red poppy from the beginning. Invited to the American Legion convention to speak about her idea for an “Inter-Allied Poppy Day,” Madame Guérin helped convince the Legion members to adopt the poppy as their symbol, and to join her by celebrating National Poppy Day in the United States the following May.

Back in France, Guérin organized French women, children and veterans to make and sell artificial poppies as a way to fund the restoration of war-torn France. As Heather Johnson argues on her website devoted to Madame Guérin’s work, the Frenchwoman may have been the single most significant figure in spreading the symbol of the Remembrance poppy through the British Commonwealth countries and other Allied nations.

Within a year, Guérin brought her campaign to England, where in November 1921 the newly founded (Royal) British Legion held its first-ever “Poppy Appeal,” which sold millions of silk flowers and raised over £106,000 (a hefty sum at the time) to go towards finding employment and housing for Great War veterans. The following year, Major George Howson set up the Poppy Factory in Richmond, England, in which disabled servicemen were employed to make the fabric and paper blooms.

Other nations soon followed suit in adopting the poppy as their official symbol of remembrance. Today, nearly a century after World War I ended, millions of people in the United Kingdom, Canada, France, Belgium, Australia and New Zealand don the red flowers every November 11 (known as Remembrance Day or Armistice Day) to commemorate the anniversary of the 1918 armistice. According to McNab, the Poppy Factory (now located in Richmond, England and Edinburgh, Scotland) is still the center of poppy production, churning out as many as 45 million poppies made of various materials each year.

In the United States, the tradition has developed a little differently. Americans don’t typically wear poppies on November 11 (Veterans Day), which honors all living veterans. Instead, they wear the symbolic red flower on Memorial Day—the last Monday in May—to commemorate the sacrifice of so many men and women who have given their lives fighting for their country.

“In Flanders Fields” by John McCrae

In Flanders fields the poppies blow Between the crosses, row on row, That mark our place; and in the sky The larks, still bravely singing, fly Scarce heard amid the guns below.

We are the Dead. Short days ago We lived, felt dawn, saw sunset glow, Loved and were loved, and now we lie In Flanders fields.

Take up our quarrel with the foe: To you from failing hands we throw The torch; be yours to hold it high. If ye break faith with us who die We shall not sleep, though poppies grow In Flanders fields.