Memorial Day was born out of necessity. After the American Civil War, a battered United States was faced with the task of burying and honoring the 600,000 to 800,000 Union and Confederate soldiers who had died in the single bloodiest military conflict in American history. The first national commemoration of Memorial Day was held in Arlington National Cemetery on May 30, 1868, where both Union and Confederate soldiers are buried.

Several towns and cities across America claim to have observed their own earlier versions of Memorial Day or “Decoration Day” as early as 1866. (The earlier name is derived from the fact that decorating graves was and remains a central activity of Memorial Day.) But it wasn’t until a remarkable discovery in a dusty Harvard University archive the late 1990s that historians learned about a Memorial Day commemoration organized by a group of freed black slaves less than a month after the Confederacy surrendered in 1865.

Back in 1996, David Blight, a professor of American History at Yale University, was researching a book on the Civil War when he had one of those once-in-a-career eureka moments. A curator at Harvard’s Houghton Library asked if he wanted to look through two boxes of unsorted material from Union veterans.

“There was a file labeled ‘First Decoration Day,’” remembers Blight, still amazed at his good fortune. “And inside on a piece of cardboard was a narrative handwritten by an old veteran, plus a date referencing an article in The New York Tribune. That narrative told the essence of the story that I ended up telling in my book, of this march on the race track in 1865.”