Richard and Lisa Stuart were walking beside the Potomac River when they noticed an odd rock in the riprap on the water's edge.

“I think that’s a headstone,” Richard Stuart remembers saying to his wife that day four years ago.

Once they started looking, they saw another. And another. With horror, Stuart discovered that a two-mile stretch of erosion control along the riverfront farm he had just purchased was full of grave markers.

A state senator, Stuart enlisted Virginia historians to figure out where they came from. The trail led upriver to the nation’s capital, and illuminated a dark truth about how Washington became the city it is today: The headstones were from Columbian Harmony Cemetery, a historic African American burial ground that was dug up and relocated in 1960 to make way for commercial development.

Now the site of the Rhode Island Avenue-Brentwood Metro station and surrounding shops and condos, Columbian Harmony had been the final resting place for a century’s worth of D.C.’s most illustrious Black citizens. Among them: Elizabeth Keckley, confidante of Mary Todd Lincoln; Philip Reid, who helped create the statue of Freedom atop the U.S. Capitol dome; and scores of Black Civil War veterans from the Union Army.

But it wasn’t just famous names. Some 37,000 people were laid to rest there between 1859 and 1960. Columbian Harmony is among at least five major African American cemeteries in D.C. that were obliterated in the past century for the sake of development.

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In this case, at least, there is an effort to atone. Virginia Gov. Ralph Northam (D) has stepped in to help Stuart, and the state has enlisted a nonprofit group to remove as many headstones as possible from the river. Through a tentative deal with Maryland Gov. Larry Hogan (R), there are plans to send many of the headstones to the relocated cemetery in Land­over, Md., and create memorials in both Maryland and Virginia.