Charles Brewer never expected to be spending Christmas Eve nearly knee-deep in the mud of northern France. Stationed on the front lines, the 19-year-old British lieutenant with the Bedfordshire Regiment of the 2nd Battalion shivered in a trench with his fellow soldiers. After Great Britain entered World War I in August 1914, many of them had expected that they would make quick work of the enemy and be home in time for Christmas. Nearly five months and 1 million lives later, however, the Great War had bogged down in intractable trench warfare with no end in sight.

Although disappointed to be far from home on Christmas Eve, Brewer at least took solace in the fact that the perpetual rain, which made moving through the trenches as much of a slog as the war itself, had finally abated on the moonlit night. All was jarringly quiet on the Western Front when a British sentry suddenly spied a glistening light on the German parapet, less than 100 yards away. Warned that it might be a trap, Brewer slowly raised his head over the soaked sandbags protecting his position and through the maze of barbed wire saw a sparkling Christmas tree. As the lieutenant gazed down the line of the German trenches, a whole string of small conifers glimmered like beads on a necklace.

Brewer then noticed the rising of a faint sound that he had never before heard on the battlefield—a Christmas carol. The German words to “Stille Nacht” were not familiar, but the tune—“Silent Night”—certainly was. When the German soldiers finished singing, their foes broke out in cheers. Used to returning fire, the British now replied in song with the English version of the carol.

When dawn broke on Christmas morning, something even more remarkable happened. In sporadic pockets along the 500-mile Western Front, unarmed German and Allied soldiers tentatively emerged from the trenches and cautiously crossed no-man’s-land—the killing fields between the trenches littered with frozen corpses, eviscerated trees and deep craters—to wish each other a Merry Christmas. Political leaders had ignored the call of Pope Benedict XV to cease fighting around Christmas, but soldiers in the trenches decided to stage their own unofficial, spontaneous armistices anyway.

Far from an organized, top-down ceasefire, the Christmas Truce instead was a series of small armistices that bubbled up from the men in the foxholes deciding to fraternize with the enemy. “We shook hands, wished each other a Merry Xmas and were soon conversing as if we had known each other for years,” British Corporal John Ferguson wrote of the encounter between his Seaforth Highlanders and German forces. “Here we were laughing and chatting to men whom only a few hours before we were trying to kill!”

“Almost always, it was the Germans who at least indirectly invited the truce,” writes Stanley Weintraub in his book “Silent Night: The Story of the World War I Christmas Truce.” That was partly because the Germans were winning the war at that point and many of their troops had worked in Great Britain before the war and could speak English.

The soldiers exchanged makeshift gifts such as cigarettes, chocolates, sausages, liquor and plum puddings and likely swapped stories about the miseries of war. German soldiers in Houplines even rolled barrels of beer they had seized from a nearby brewery across no-man’s-land to the British trenches where, according to British soldier Frank Richards, they raised toasts to one another’s health and united in agreement that “French beer was rotten stuff.”

In some cases, the strip of death between the trenches even came alive with pick-up soccer games as soldiers navigated around the shell craters and barbed wire in no-man’s-land. “We marked the goals with our caps,” German Lieutenant Johannes Niemann recalled. “Teams were quickly established for a match on the frozen mud, and the Fritzes beat the Tommies 3-2.” Where soldiers lacked a real leather ball to kick with their waterlogged boots, tin cans and small sandbags sufficed.

Not every fighting man, particularly those who had just seen comrades killed in action, felt moved by the Christmas spirit. Gunfire continued to be exchanged in certain locations along the front, and in some unfortunate cases soldiers were killed by enemy fire as they emerged from the trenches in the hope for a day of peace. The unsanctioned truce concerned high-ranking officials, afraid that their men might lose the will to fight, and outraged others, including one young German corporal who would launch the next world war. “Such a thing should not happen in wartime,” Adolf Hitler scolded his fellow soldiers. “Have you no German sense of honor left?”

As the sun set on Christmas, the fighters retreated to their respective trenches. A few ceasefires held until New Year’s Day. In most locations, however, the war resumed on December 26. At 8:30 a.m. in Houplines, Captain Charles Stockwell of the 2nd Royal Welch Fusiliers fired three shots into the air and raised a flag that read “Merry Christmas.” His German counterpart raised a flag that read “Thank you.” The two men then mounted the parapets, saluted each other and returned to their sodden trenches. Stockwell wrote that his counterpart then “fired two shots in the air—and the war was on again.”

The guns quickly extinguished the brief flicker of peace, and British Expeditionary Force commander John French issued orders that such a grassroots ceasefire should never happen again. When Christmas returned to the trenches in 1915, the truce did not. Holiday cheer was in short supply like so many other rations after a year that saw the unleashing of poison gas, the sinking of the British ocean liner Lusitania by German U-boats and the deaths of millions more on and off the battlefield.

The guns of World War I did not fall silent again until the signing of the armistice on November 11, 1918. The Christmas Truce, however, provided an unforgettable memory for many such as the British soldier who confessed in a letter the following day, “I wouldn’t have missed the experience of yesterday for the most gorgeous Christmas dinner in England.”