A "folly," to an English country gentleman of times long past, was a contrived architectural element -- a medieval turret, a Gothic spire, a classical "ruin" -- inserted in the rambling landscape of his estate to impart surprise, delight or even awe. The word had ambivalent connotations: It highlighted the owner's eccentricity, or foolishness, but at the same time celebrated his wealth, status and taste.

Washington now has a folly worthy of the name. Comprising 22 Corinthian sandstone columns splendidly set atop a gentle rise of ground at the National Arboretum, it is an inspiring but thoroughly improbable sight. One rounds the bend in one of the arboretum's many drives and there it is, an apparition as American as, well, 170-year-old classical columns.

The story of its placement and construction -- the official dedication is Thursday -- combines American pragmatism, willfulness and ingenuity. This folly was erected in the cause of historic preservation with nearly $2 million from a variety of private sources. Originally ornamenting the Capitol's East Front, the columns were orphaned during the expansion three decades ago, plopped unprotected in a local federal hideaway and then adopted by the late Ethel Garrett, a woman of some wealth, good connections and a vision to raise the columns at the arboretum.

This location is eccentric, but fine. The National Capitol Columns, as they're now called on maps of the arboretum grounds, have nothing to do with the research mission of the institution, but they make a swell adornment. Perhaps they will lure more visitors to "Washington's best-kept secret," as arboretum Director Henry M. Cathey, with apt exasperation, refers to his 444-acre domain in the northeast quadrant.

In Garrett's initial notion the columns were to be placed atop Mount Hamilton, the arboretum's highest point, where they would rank with the city's other monuments on high ground, including the Capitol, the Shrine of the Immaculate Conception and the Washington Cathedral. This placement, however, would very nearly have denuded the hill of its trees -- an obvious no-no for an institution devoted to the preservation and improvement of the natural environment, and a providential one.

After Garrett's singular crusade had successfully overcome numerous legal and bureaucratic obstacles, in the mid-1980s English landscape gardener Russell Page selected the more appropriate site facing a broad, undulating meadow. Page died before completing a design; the Alexandria office of the landscape architecture firm of EDAW, with Russ Hanna as principal in charge and Pat Faux as project designer, completed the effort, altering Page's sketchy conception in several key respects.

The most important of the changes was to reshape Page's reflecting pool, transforming a long rectangle into a more nearly square one that strikingly reflects the entire composition when seen from one point of view.

Where Page had foreseen a more picturesque, random arrangement of flagstones as a ground surface, EDAW provided a simple grid of aged marble slabs -- saved from the Senate-side stairs of the Capitol's East Front. Likewise, Page's notion of exotic plantings -- olive trees and gray-green shrubs -- was eliminated in favor of a plainer, less obtrusive arrangement of trees on the hillside.

"We felt that this was a uniquely American artifact," Faux recalls, "and we wanted to avoid at all costs the impression that the American Capitol had gone to ruin."

Of course, this entire installation is something of a romantic ruin. But with one exception, it's not excessively doctored up. The exception proves the rule, perhaps: It's the placement of a leftover column base and Corinthian capital (from one of two original columns that couldn't be reused) as a western terminus of a view from the hilltop platform supporting the columns. The view is picturesque, all right, but it's also symbolically misleading -- the way it is placed suggests that it's the main point of a visit.

Then again, it is not something to get wildly upset about. This is an earnest, all-American (or at least all-Washington) folly, but it is a folly just the same. Indeed, it's a little miracle that what could have been sheer hokum turned out to be so pleasing. Spectacularly alluring from afar, the columns are entrancing close up, their capitals vigorously cut, their Aquia Creek sandstone shafts (stripped of layers of white paint) beautifully illuminated by the soft afternoon sun.

Most important, Benjamin Henry Latrobe's columns now define a quiet, comforting, contemplative place -- reward enough for a nice walk across the meadow. Cathey says the place will sound good and smell good too when the water in Page's Alhambra-inspired fountain is turned on and the thyme plants in the earthen interstices between the marble slabs are in bloom. The herbs are a fine, subtle touch -- they complement the old stones. And they won't be trimmed, in accordance with Cathey's philosophical motto, "Tough plants for tough times."

Latrobe, the architect who designed the columns, doubtless would be angered by their removal from the Capitol -- an unambiguous folly, that -- and probably he'd be astonished at their new location and use. But it is also likely that he would be pleased. Recycled, they make a curiously affecting statement in one of the city's most appealing natural settings.