After John II of France was captured by the English in 1356, he paid 1 million gold crowns for his ransom and promised to pay 2 million more. As a guarantee he offered his son Louis as a hostage. When word came that Louis had escaped, John voluntarily returned to captivity in England, citing reasons of “good faith and honor.” He died there in 1364.

In 1916, after two years in a German prisoner-of-war camp, British Army captain Robert Campbell received word that his mother was dying of cancer. He wrote to Kaiser Wilhelm II asking permission to visit her, and was given two weeks’ leave on condition that he return afterward. Campbell went to England, spent a week with his dying mother, then returned to confinement in Germany, where he remained until the war ended.

“Captain Campbell was an officer, and he made a promise on his honor to go back,” said historian Richard Van Emden, who uncovered the episode while researching his book Meeting the Enemy. “Had he not turned up there would not have been any retribution on any other prisoners. What I think is more amazing is that the British Army let him go back to Germany.”