German troops in Flanders, accessible from home by land, received, along with their wooden gift boxes decorated with a wreath and a Flammenschwert - a flaming sword - tabletop-size Christmas trees with candles conveniently clamped to the branches. The law of unintended consequences activated itself. On Christmas Eve, as darkness came early, the Germans - at some hazard - placed trees atop trench parapets and lit the candles. Then they began singing carols, and though their language was unfamiliar to their enemies, the tunes were not. After a few trees were shot at, the British became more curious than belligerent, and crawled forward to watch and to listen. And soon they began to sing.

By Christmas morning, no man's land between the trenches was filled with fraternising soldiers, sharing rations, trading gifts, singing, and - more solemnly - burying the dead between the lines. (Earlier, the bodies had been too dangerous to retrieve.)

The high brass on both sides quickly determined that they could not let the situation develop. In the national interest, the war had to go on. Peace has always been more difficult to make than war, but it was materialising. Under threat of court martial, troops on both sides were ordered to separate and restart hostilities. Reluctantly, they drifted apart. General Sir Horace Smith-Dorrien's order to II Corps from his cushy rear-area headquarters read: "On no account is intercourse to be allowed between opposing troops. To finish this war quickly we must keep up the fighting spirit."

A Christmas truce seems in our new century an impossible dream from a more simple, vanished world. Peace is indeed, even briefly, harder to make than war.