British and German soldiers stopped fighting to sing carols and swap gifts

Around Christmas 1914, along stretches of the Western Front, roughly 100,000 British and German troops climbed out of their trenches on their own initiative, exchanged food, tobacco and souvenirs, and buried their dead together in no man's land. Military command on both sides had explicitly forbidden fraternising with the enemy. It never happened again at that scale in the war's remaining four years.

— Stanley Weintraub, Silent Night: The Story of the World War I Christmas Truce — 2001
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