One of Washington's earliest historic artifacts can be found not in the National Archives, but in Frank Ruddy's front lawn.

There, a few feet from his Chevy Chase doorstep, sits a short, square stone. For an inanimate object, the 900-pound gray slab boasts quite a following: Ruddy often finds strangers in his yard hovering over it, snapping pictures.

The stone was there long before he moved in Oct. 13, 1981. In fact, the little chunk of history is as old as the country itself -- eight years older than the opening of the White House, 16 years younger than the signing of the Declaration of Independence.

It was set there in 1792 and hasn't budged, one of the oldest and most oddly located relics of America's past. But Ruddy still has to mow the lawn. His strategy is simple, he said: "Don't crash into it."

The stone that Ruddy's lawn mower must dodge is one of 40 boundary markers delineating the exact border of the District of Columbia. The markers were placed at one-mile intervals in 1791 and 1792, forming the diamond-shaped territory of the young nation's capital. Most of the stones remain in place today, thanks to the vigilance of gray- haired boundary buffs and a little bit of luck.

Uncle Sam's glistening marble monuments dominate the skies of Washington, but none is older than the sandstone markers that rise roughly two feet off the ground. Surveyors working under the direction of George Washington cleared a path through the Virginia and Maryland countryside beginning in February 1791, forming a square 10 miles to a side.

Leading the effort was Andrew Ellicott, the nation's preeminent surveyor. Ellicott used the most precise geodetic instruments available, several of which are on display at the Smithsonian's Museum of American History. He also enlisted the help of Benjamin Banneker, a free black who was an astronomer and mathematician.

Each marker was inscribed with the magnetic compass reading and the words "Jurisdiction of the United States" on the side facing the District. The stones came from the same Stafford County quarry that later produced the building blocks for the Capitol and the White House.

In a city of easy-to-spot landmarks and other tourist attractions, the District's boundary stones are perhaps the most difficult to find. No road signs point the way. After the federal government ceded land back to Virginia in 1846, the markers on that side of the Potomac ended up in a handful of jurisdictions. With local maps offering no help, people sort of stumble into the stones. Literally.

Southwest 3 resides in the parking lot of the First Baptist Church in Alexandria. Northwest 1 sits behind the toolshed of auto mechanic Vernon Hall on Powhatan Street in Arlington County. "The stone will be here long after I'm gone," said Hall, 46. Like others who have boundary stones in their yards, Hall said he doesn't mind curiosity- seekers, though knocking is appreciated.

Southwest 6 makes its home in the traffic median on South Jefferson Street where Arlington meets Fairfax County. It survived a snowplow mishap several years ago.

Devoted fans of the markers have worked to preserve and protect this American Stonehenge connecting Washington's present with its past.

"The boundary stones are the oldest monuments in Washington," said Gayle Harris, a member of the District of Columbia Daughters of the American Revolution.

Since 1916, DAR members have cleaned and otherwise looked after the stones, erecting wrought-iron fences around many and even penning occasional poems in tribute. Others, too, have pitched in, including the National Park Service and historical groups from across the region.

It was inevitable perhaps -- this being Washington, after all -- that a committee would be formed to look after the stones: the Nation's Capital Boundary Stone Committee wants the stones listed as national historic landmarks and seeks to have the Park Service assume responsibility for them. However, questions linger about who owns the stones on private property and in Virginia.

"These things essentially have gone unnoticed, unchaperoned, unmaintained for 210 years now," said committee Chairman Ric Terman.

Some stones have held up better than others. A few have had to be replaced, though vandals and bulldozers have taken more of a toll than has Mother Nature.

A purloined plaque from the West Corner Stone, located in a park in Falls Church, turned up at a flea market in Danville, Va.

One stone, Northeast 1 on Eastern Avenue, remains missing and unreplaced; it was last seen on a truck in 1952, apparently mistaken for rubble by a construction crew.

Southeast 4 on Naylor Road also was AWOL for a time, but in 1991 members of the Maryland Society of Surveyors found it in a nearby basement. A man had saved the marker after a traffic accident, and it now sits in the Silver Spring garage of society member Dave Doyle, waiting once more to become a small fixed point in an ever-changing world.

GETTING THERE: Though several of the historic markers are on private property, some are in public places or viewable from sidewalks. The West Corner Stone, for example, is in a park in Falls Church. From Washington, take Interstate 66 west, exiting at Sycamore Street. Turn left onto Washington Boulevard and make another left onto Fairfax Drive. Turn right onto Meridian Street and the park will be on the left.

HOURS: Stones never sleep, so no appointments are necessary. No admission fees, either.

PARTICULARS: Almost all of the original 40 stones set down by Andrew Ellicott 210 years ago, marking the boundary of the District of Columbia, remain in place today. The stones were placed one mile apart -- unless that meant in a streambed or on unstable ground -- and numbered clockwise from corner to corner. Fourteen of the historic markers are in Virginia, and 26 sites border Maryland. The Daughters of the American Revolution began erecting fences in 1916 to protect the markers and help guide visitors to them. However, a full tour is greatly aided by the sharp eyes of a boundary marker expert.

For more information about the stones and where to find them, call 703-960-1361.