"Silent night, holy night. All is calm, all is bright," the Christmas carol was sung on the north lawn at the UN headquarters in the chilly Friday afternoon.
It is for the "Christmas truce," a series of unofficial cease-fires that took place around Christmas 1914 during World War I, in which British and German soldiers stopped fighting for a day, exchanged greetings and sang carols in trenches of the Western Front. Some of them were friendly enough to play football together.
The United Nations held a special event to commemorate the centenary of the truce, which UN Secretary-General Ban Ki-moon referred to as "quite extraordinary, unchoreographed."
"To this day, the events of Christmas 1914 give us hope that enmities can be forgotten, and that former enemies ... can become great allies," Ban told the event.
"Tragically, the world found itself at war again (in WWII). The United Nations rose from those ashes, and next year will celebrate its 70th anniversary," he added.
After Ban's speech, diplomats who gathered on the lawn sang a stanza of "Silent Night" in English and German, and then they lined up to take soccer penalty shots, which cheered the crowd.
During the event, British and German ambassadors read extracts of letters written by British and German soldiers at the time to help rebuild scenes of the truce.
"The Germans sang 'Stille Nacht,' it sounded well. Then our men sang 'Silent Night,' it sounded so well too," wrote a British officer stationed at the Western Front in 1914.
The German ambassador read a letter written by Josef Wenzl, a soldier from the 16th Bavarian Reserve Infantry Regiment, to his parents on Dec. 28, 1914.
"Between the trenches the bitter and hated enemies were standing around the Christmas tree singing Christmas songs," he wrote. "I will never forget this sight for as long as I live."
Wenzl was killed in action on May 6, 1917. Like millions of others who lost their lives in WWI, he went to sleep "in heavenly peace," as the Christmas carol goes.