One of the most important antecedents of the modern Memorial Day was a Decoration Day organized by freedman's relief organizations and formerly enslaved people in Charleston, South Carolina, on May 1, 1865. One of a series of celebrations in the destroyed city to mark the end of the war, this event was orchestrated by the African American citizens of Charleston to mark and decorate the graves of the 257 Union prisoners who died at the Charleston Race Course, which had been converted to a Confederate prison. Thousands of freedmen, including almost 3,000 black schoolchildren, gathered to decorate the graves with flowers and beautify the graveyard, building an enclosure and an arch labeled, "Martyrs of the Race Course" in what is now Hampton Park. Scholar David Blight has christened this event the first Memorial Day: "What you have there is black Americans recently freed from slavery announcing to the world with their flowers, their feet, and their songs what the War had been about. What they basically were creating was the Independence Day of a Second American Revolution," he said in a recent speech.
Via the Smithsonian: the origins of Memorial Day, a remembrance which grew out of the Civil War but -- I didn't know this -- didn't become a federal holiday until 1971, only two years before I was born.