On the side of a wind-swept field covered with scorpion weed, a simple wooden cross marks a unique event in football history.

At its base, amid wreaths of poppies, lie a smattering of balls and various club pennants, all in remembrance of the Christmas Truce of 1914.

A century ago on Christmas Day, German and British enemies left their World War I trenches and headed into no man's land in a few scattered locations on the Western Front for an unofficial truce among soldiers. Some eyewitness accounts say they were highlighted by something as remarkable as a few football kick-abouts.

"Suddenly a Tommy came with a football," wrote Lt. Johannes Niemann of Germany, referring to a British soldier. "Teams were quickly established for a match on the frozen mud, and the Fritzes beat the Tommies 3-2."

If not fully-fledged matches, other soldier's diaries and various reports also spoke of balls being kicked about in friendship.

"A huge crowd was between the trenches. Someone produced a little rubber ball so of course a football match started," Lt. Charles Brockbank of Britain's Cheshire Regiment wrote in his diary, which is part of "The Greater Game" exhibit at the National Football Museum in Manchester.

The proponents of the sport have cherished that day as historic proof that there is little that can better bridge man's differences than football.

This Christmas, the British supermarket chain Sainsbury's has taken the idea and turned it into a blockbuster ad, showing opposing soldiers living the truce amid a football match at the center of the heart-tugging, some say sanitized, view of that Great War day.

It is that unique mood of brotherhood that Michel Platini, the president of the Union of European Football Associations (UEFA), plans to underscore on Thursday. He plans to unveil a Christmas truce monument on the former battlegrounds known as Flanders Fields in western Belgium, scene of some of the most horrendous killing.

"Together, they performed simple acts of reconciliation, culminating in the discovery of a shared language: football," Platini wrote to European Union leaders early this year.

For those involved, it was most of all a yearning for a sense of normalcy, however momentarily, that pushed them over the edge of their trenches, unarmed.

The war had started on Aug. 4 when the German invasion of Belgium kicked off a series of events which quickly pitted the German and Austro-Hungarian empires against Britain, France, Russia and several allies.

Germany swept into most of Belgium and northern France and even threatened Paris before the frontline was settled. Armies entrenched themselves for most of the next four years. At the time, though, the prevailing expectation on both sides had been to be home for Christmas.

When that didn't happen, an early sense of euphoria quickly made way for unrelenting gloom. It set the stage for the Christmas truce and those magic kick-abouts.

Football players themselves had been involved in the fighting from the early days. Of the 5,000 professional players at the time, about 2,000 joined the armed forces. Sometimes whole lineups signed up at the same time to create what became known as the Footballers' Battalions. London club Clapton Orient, now known as Leyton Orient, alone had about 40 players and staff joining the war effort, all following the steps of their team captain.

Scotland's top team at the time, Edinburgh club Hearts, had its whole team join the British army one month ahead of that Christmas, a move which inspired others to join, said Peter Francis of the Commonwealth War Graves Commission. Seven members of that team were killed in the war.

One of the first footballers killed in the war was Larrett Roebuck, a Huddersfield defender. After playing for his team in a 1-0 victory at Leicester Fosse early in the 1914-15 season, he left for the Western Front and was killed in action on the eve of the first Battle for Ypres, a few kilometers from that patch of land in Ploegsteert.

"The story is that he set off running across the field with the machine guns going," said Roebuck's grandson, Frank Wood. "His friend saw him go down but he couldn't stop to help him. With the fight like that, you couldn't stop."

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Virginia Mayo contributed to this report.

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