In the shadow of the Smithsonian "Castle" stands a neoclassical urn atop a handsome marble base. It gets barely a glance from the tourists milling around the Mall, but it is Washington's only monument to Andrew Jackson Downing.

You know. Andrew Jackson Downing. The guy who originally landscaped the Mall, back in 1850. Never mind that the Mall doesn't bear much resemblance to Downing's plan. He did it, it's history and that's what monuments are for.

The presidents get all the glory in Washington, along with the assorted military heroes lucky enough to have their monuments placed in the center of traffic circles or close to Metro stops that will ever bear their names.

But for every Jefferson Memorial and McPherson Square there's a granite remembrance of some other soul whose contribution to history has become dusted with obscurity, a fate worse than pigeon droppings.

Barely a stone's throw from the Lincoln Memorial in West Potomac Park stands an elegant sculpture dedicated to John Ericsson, the developer of the screw propeller and designer of the ironclad Monitor. Dr. Samuel Hahnemann, father of homeopathy, is memorialized at Scott Circle, although the medical science he pioneered has largely fallen out of favor.

And among the memorials at Meridian Hill Park is an allegorical sculpture honoring Lt. Cmdr. William Henry Schuetze, whose foremost claim to fame appears to be that he graduated first in the 1873 class at the U.S. Naval Academy, where he made friends with a man wealthy enough to commission a statue.

Whimsical as they now appear, the monuments stand as testament to a time when it was easier to put statuary on public land in Washington. Today, it's tough to find a suitable spot for a bronze plaque, let alone a larger-than-life equestrian statue or marble fountain with water-spouting nymphs.

"It gets sticky, especially in the memorial core area on the Mall," said Sandra Alley, spokesman for the National Park Service's capital regional office. "We don't have enough space left."

But if there's one thing harder than finding a spot for a new monument, it's getting rid of an existing one. That hasn't been tried since the Kennedy administration, when Interior Secretary Stewart L. Udall launched a campaign to remove "excess sculpture."

Udall complained that "those who attempt to find in our memorials some sort of waypost on the road of American history must indeed be puzzled when confronted with a statue honoring a Gaucho leader in the Uruguay revolution for independence but none of Thomas Paine or Nathan Hale."

The secretary apparently was unaware that Judiciary Square already boasted a statue of Hale, and South Americans were not amused by his reference to Jose Artigas, whose statue was purchased as a gift to the United States by contributions from Uruguayan schoolchildren.

Nonetheless, statues are occasionally removed. Some are placed on "permanent loan" to an institution in another city. Some, like the Titanic Memorial that was plucked off Rock Creek Parkway to make way for the Kennedy Center, find new homes. (It's in Washington Channel Park now, a good distance from the other Titanic memorial, the Butt-Millet Memorial Fountain, which graces the Ellipse. The fountain honors President William Howard Taft's military aide, Maj. Archibald Wallington Butt, and artist Francis Davis Millet, who went down with the ship.)

And some just disappear, like the Cuban Friendship Urn.

The elaborately carved urn was made from the hurricane-damaged remnants of a marble column that once stood in Havana in honor of the victims of the USS Maine. Cuba gave it to President Calvin Coolidge in 1928 and it was given a spot in West Potomac Park.

The urn was whisked away in 1963 -- ostensibly because of construction on the Roosevelt Bridge -- and the park service isn't sure where it went.

"That kind of went the way of Cuban-American friendship," said Alley. "It's lost. Not like someone lost it, but it's missing."

Another one that's missing, or at least partly so, is the McMillan Fountain, a Beaux-Arts sculpture erected by Michiganders in 1913 in honor of Sen. James McMillan. The gesture seemed appropriate -- McMillan took a special interest in beautifying Washington and established the commission that eventually recommended restoring Pierre L'Enfant's 1792 plan for the city.

But the fountain was removed from its spot at 1st and Channing streets NW for construction work in 1941, and now is "literally scattered around Washington," Alley said. Most of the fountain, including its ornate base, is in storage in one place or another; part of it is on display in the District's Crispus Attucks Park.

Construction work appears to be the only dynamite strong enough to dislodge a monument, whatever its redeeming historical value.

A handsome cast iron Victorian fountain honoring Commodore Thomas Truxtun was originally erected in 1877 in a city park at Mount Vernon Place. When the park gave way to the old District of Columbia Public Library, the fountain was moved to North Capitol Street and Rhode Island Avenue NW, which became Truxtun Circle.

Truxtun, an 18th century privateer who later turned his sailing skill to military advantage as the captain of the USS Constellation, might thus have been spared creeping obscurity.

Alas, when North Capitol Street was widened in 1946, Truxtun Circle was obliterated. The fountain is in storage, Alley said, and there are no plans to erect it elsewhere. "It is in kind of dilapidated condition," she said.