In this image provided by the Imperial War Museum, World War I German and British soldiers stand together on the battlefield near Ploegsteert, Belgium, in December 1914. (Cyril Drummond/AP)

Christmas 1914 fell on a Friday. At the White House, President Woodrow Wilson had Christmas dinner at 7. Children went sledding on snow-packed streets in Georgetown. And umbrellas at Lansburgh’s were on holiday sale for $1.59.

America, for the moment, was at peace.

But Christmas Day in Europe came four months into the carnage of World War I. And early that morning, British Capt. Edward Hulse, 25, of the Scots Guards, peered across the no-man’s-land of the Western Front at an astonishing sight:

Four unarmed German soldiers who had climbed out of their trenches were advancing over the shell-cratered field toward the British lines. Prior to this, anyone who showed a finger above the trenches risked having it shot off. But now there was no firing.

Mystified, Hulse, dressed in an overcoat and an old stocking cap, went out to meet them. By what orders had they come, he asked. “None,” he said they replied. “They had just come over out of good will.”

People dressed as British and German soldiers pay tribute at a memorial for the no-man’s-land football match between British and German soldiers, during a re-enactment of the so-called Christmas Truce in Warneton, Belgium, on Dec. 21. (Stephanie Lecocq/European Pressphoto Agency)

“They . . . thought it only right to . . . wish us a happy Christmas,” Hulse wrote his mother, Edith, three days later.

What followed, he wrote, “was the most extraordinary Christmas . . . you could possibly imagine.”

Hulse was describing the legendary Christmas truce — the impromptu, unofficial, mass cease-fire that broke out among warring German, British, French and Belgian troops in December 1914.

A century ago this month, all along the Western Front, where the German army had fought the allies in battles that already had killed tens of thousands, informal cease-fires were declared.

Soldiers from both sides cautiously left their trenches, exchanged shouts of greeting and songs, held up holiday signs and then began to mingle in the frozen dead zone between the lines.

Near places such as Ploegsteert Wood, in Belgium, where a British attack had failed disastrously seven days earlier, foes mingled and shook hands. Near Armentieres, in France, the scene of bitter fighting in October, a German juggler performed.

A German violinist performed Handel’s haunting Largo for the French. Victor Granier, of the Paris Opera, sang the carol “O Holy Night” in French for the Germans.

In this image provided by the Henry Williamson Society, a letter from World War I soldier Private Henry Williamson to his mother dated Dec. 26, 1914. (AP)

German soldiers sang “Stille Nacht, Heilige Nacht,” while the British sang “Silent Night, Holy Night.” Everyone sang “Auld Lang Syne.”

Souvenirs were exchanged — cigars, cigarettes, belt buckles, uniform buttons, tins of bully beef and jam. Germans gave the British barrels of beer. A German barber who had worked in Britain clipped the hair of a former customer.

Pickup soccer games were played with makeshift balls, and scores were kept. In some cases, photographs were taken.

In many places, warfare ceased.

The truce is less known in the United States, which did not enter the war on the side of the allies until 1917. But in Europe this month it has been remembered at soccer games, with the unveiling of a memorial in Britain, and a controversial three-minute commercial by the British supermarket company Sainsbury’s.

Historian Stanley Weintraub, whose 2001 book, “Silent Night,” recounts the truce, said soldiers in the trenches, like Hulse, were amazed by what was happening.

“You wouldn’t believe this,” he said they wrote their relatives. “It was like a waking dream.”

Hulse, whose writing appears in the 1930 book “War Letters of Fallen Englishmen,” wrote his mother: “It was absolutely astounding, and if I had seen it on a cinematograph film I should have sworn that it was faked!”

Sgt. Bob Lovell, of the 3rd London Rifles, wrote after a soccer match with the Germans: “I can scarcely credit what I have seen and done. It has indeed been a wonderful day.”

The war, which had started the previous summer, had resulted in astounding bloodshed. Mechanized weaponry and antique tactics had caused huge death tolls on both sides.

Fighting around the Belgian town of Ypres that fall had killed an estimated 8,000 British soldiers and almost 20,000 Germans, and it left the sides mired in the new misery of trench warfare.

It was a world of “lice, rats, barbed wire, fleas, shells, bombs . . . corpses, blood . . . (and) filth,” the German soldier and future expressionist painter Otto Dix wrote, according to Weintraub’s account. “It is the work of the devil.”

In some places, the lines were less than 100 yards apart, and there was constant sniping, raiding and grenade-throwing along with regular artillery fire.

Death was always at hand, and no-man’s-land was strewn with moldering bodies.

Hence the surprise when quiet began to descend over the battlefields on Christmas Eve.

“There was a kind of an . . . intangible feeling extending across the frozen swamp between the two lines, which said ‘This is Christmas Eve for both of us — something in common,’ ” British Lt. Bruce Bairnsfather, 26, wrote in a 1916 memoir, “Bullets & Billets.”

Another British soldier, Albert Moren, of the 2nd Queen’s Regiment, later remembered that “it was a beautiful, moonlit night, frost on the ground, white almost everywhere. . . . I shall never forget it. It was one of the highlights of my life.’’

Not all units participated in the truce, and not all soldiers agreed with it. One such soldier was a young German corporal named Adolf Hitler, Weintraub recounts.

Although Hitler’s unit was not on the front lines that Christmas, the future Nazi leader said of the truce: “Such a thing should not happen in wartime. Have you no German sense of honor left at all?”

Weintraub said a half-hearted attempt at a truce the following Christmas failed, and there were no more Christmas truces during the war.

He added that there were none in World War II. Indeed, at Christmastime during the 1944 Battle of the Bulge, Nazi soldiers used a loudspeaker to tell beleaguered Americans that they were about to die, he said.

The 1914 truce petered out in the days after Christmas. Often each side warned the other that superiors had ordered the fighting to resume.

A British soldier from London, George Eade, recalled that a German who had lived in London told him as they parted: “Today we have peace. Tomorrow, you fight for your country. I fight for mine. Good luck.”

Weintraub said that many of the men who witnessed Christmas 1914 probably did not survive the conflict. “Unfortunately, a lot of the people who were in the truce, and friendly with each other, could not last out four years of war,” he said.

Back in snowy Washington that day, President Wilson and his family gathered around a Christmas tree in the White House second-floor library, according to news reports

The Washington Post said it took heart from the world’s ability to mark Christmas amid a global war.

“There is either something whimsically hopeless in this, or else something very encouraging,” the newspaper said. “Mixed with the brutality of war is a spirit whose supremacy may one day bring war to an end.”

Three months later, on March 12, 1915, Hulse, of the Scots Guards, who left one of the best accounts of the Christmas truce, was killed in action at Neuve Chapelle, France.