Dozens of headstones from a historic African-American cemetery in the nation’s capital that were used for erosion control along the Virginia shoreline of the Potomac River are being relocated to a memorial garden in Maryland.

Virginia Gov. Ralph S. Northam, Maryland Gov. Larry Hogan and Washington Mayor Muriel Bowser attended a ceremony in Caledon State Park in King George, Va., on Monday to mark the transfer of the first 55 headstones from Virginia to Maryland, officials said. The grave markers will be part of a memorial garden at National Harmony Memorial Park in Prince George’s County, Md., honoring the 37,000 people buried at the original cemetery.

The Columbian Harmony Cemetery was established in 1859 and was the most prominent burial site for African-Americans in Washington. Among the people buried there were Elizabeth Keckly, a former slave who became a seamstress and trusted confidante of President Abraham Lincoln’s wife, Mary Todd Lincoln; Osborne Perry Anderson, the only African-American survivor of John Brown’s raid on Harpers Ferry in October 1859; Mary Ann Shadd Cary, America’s first African-American female newspaper editor in 1853; and Philip Reid, a foundry worker who helped build the Statue of Freedom at the U.S. Capitol, officials said.

The cemetery, however, was moved in the 1960s to make room for development, including the Rhode Island Avenue-Brentwood Metro station. Remains were moved to a memorial garden in Maryland, but the gravestones were sold or given away, officials said.

Grave markers ended up along a 2-mile stretch of the river in King George County, where Virginia Sen. Richard Stuart discovered them in 2016 while exploring a property he had just purchased. Historians helped Sen. Stuart to learn about the origin of the gravestones and he then worked with other state leaders to return them to a proper memorial site.

Officials from Virginia, Maryland and the District of Columbia are working with History, Arts and Science Action Network, a restorative justice nonprofit organization based in Hyattsville, Md., that has been working with descendants and researching the stories of those buried in the cemetery.

This fall, National Guard members from Virginia and Maryland will recover more headstones in the area where the first artifacts were found, officials said. Virginia approved $4 million for recovery and restoration of the gravestones and the creation of a shoreline memorial, Gov. Northam’s office said.