Correction: An earlier version of this story incorrectly referred to Benjamin Banneker as a freed slave. Banneker was born free in Balimiore. The story has been corrected.

Daughters of the American Revolution and Masons from the Most Worshipful Prince Hall Grand Lodge of the District participate in the May 2 rededication of Boundary Stone SE. It was laid by Andrew Ellicott and Benjamin Banneker in 1792. (Hamil Harris/The Washington Post)

In the summer of 1790, the U.S. Congress authorized President George Washington to select a 100-square-mile site along the Potomac River as the new nation’s capital. A year later, Continental Army Maj. Andrew Ellicott, joined by Benjamin Banneker, a free African American and self-taught mathematician, was commissioned to carve out the boundaries of what would soon become Washington, D.C.

As a way of clearly demarcating the new city from Maryland and Virginia, the two men began planting 40 limestone markers along the new borders in 1791. These boundary stones, as they came to be known, were planted every mile, creating the diamond-shaped swath of land that marked the original District’s borders.

“These stones are our nation’s oldest national landmarks,” said Sharon K. Thorne-Sulima, regent for the Martha Washington chapter of the D.C. Daughters of the American Revolution.

Now, 223 years later, a team lead by Thorne-Sulima’s chapter is working to restore 26 of the boundary stones along the District-Maryland border. The group is in the middle of an effort to raise more than $50,000 to preserve the stones, which are six feet in length. Volunteers hope to complete the effort later this year. There is also a separate effort to restore the 14 boundary stones in Virginia, which are part of original city land that was retuned to the state in 1846.

“Our historic preservation staff has been working over the past several years to make this project happen,” said David Maloney, state historic preservation officer in the D.C. Office of Planning. “We have partnered with DDOT [District Department of Transportation] and the NPS’s [National Park Service] Historic Preservation Training Center to fully restore these important historic artifacts.”

The rededication ceremony on May 2 of Boundary Stone SE6. There were 40 stones around the original borders of Washington, DC. (Hamil Harris/The Washington Post)

The conditions of the stones vary widely. In some cases they have been buried by brush. In other cases they have weathered 200 years of elements well. Each stone, which some liken to mini-Washington monuments because of their shape, is inscribed with “Jurisdiction of the United States” on the side of the stone facing the District. The opposite side has “Maryland” or “Virginia.” engraved on the side facing that state.

The 40 stones are anchored by four stones at each point of the original city’s boundaries, illustrating how expansive Washington’s vision was for the city: the East stone is located at Eastern Avenue and Southern Avenue in Northeast; the West stone is at the intersection of Meridian and West streets in Falls Church; the South stone is under water at the Jones Point Lighthouse in Alexandria; and the North stone is at the intersection of East-West Highway and 16th Street in Northwest.

Each time a stone is successfully restored, Thorne-Sulima’s group holds a ceremony presided over by a local group of Freemasons from the Most Worshipful Prince Hall Grand Lodge of the District of Columbia. Earlier this month, a group of volunteers gathered around stone SE6 in Southeast Washington and discussed the conditions of the 26 stones slated for restoration.

“Some of the stones were cleaned, some had fences that were repainted, some stones needed to be reset because they are six feet tall with three feet below the ground,” Thorne-Sulima said. “Four stones were severely damaged or lost, and replicas have been created.”

The first stone was placed April 15, 1791, by George Washington during a ceremony in which corn, wine and oil was poured on the stone. That Masonic ritual was repeated at the ceremony earlier this month.

Thorne-Sulima said that she considers boundary stones the oldest of federal monuments. She added that Washington had initially included Old Town Alexandria within the District’s limits, because it was one of the four busiest ports in the country.

“We are all about historic preservation,” she said. “One of the three points of the DAR mission is historic preservation, along with education and patriotism.”

The May 2 rededication ceremony for Boundary Stone SE6, laid by Andrew Ellicott and Benjamin Banneker in 1792. (Hamil Harris/The Washington Post)