obelisk in Washington, D.C. (Washington), honouring George Washington (Washington, George), the first president of the United States. Constructed of granite faced with Maryland marble, the structure is 55 feet (16.8 metres) square at the base, 555 feet 5 inches (169.3 metres) high, and weighs an estimated 91,000 tons. The shaft's load-bearing masonry walls are 15 feet (4.6 metres) thick at its base, tapering to a thickness of only 18 inches (46 cm) at the top. At its completion in 1884 it was the world's tallest man-made structure, though it was supplanted by the Eiffel Tower just five years later. It remains the world's tallest masonry structure.

Celebrations of the centenary of Washington's birth rekindled interest in a monument. In 1833 the Washington National Monument Society, chartered to select a design for an appropriate memorial to the first president, chose a plan by Robert Mills (Mills, Robert) for a 600-foot- (183-metre-) tall obelisk with a circular base complete with 30 Doric columns. The sheer weight of the proposed monument required moving the site from the location specified in L'Enfant's design to a point 350 feet (110 metres) to the northeast, thereby slightly disrupting the axial relationship to the other buildings. It was hoped that Washington's remains would eventually be moved from their burial location at Mount Vernon in Virginia and reinterred at the memorial.

Construction did not begin until 1848, and the cornerstone was laid during ceremonies on the Fourth of July. In attendance were George Washington Parke Custis, Washington's step-grandson, as well as President James K. Polk (Polk, James K.) and Congressman Abraham Lincoln (Lincoln, Abraham). Financial and political difficulties plagued the project from the start and led to major architectural modifications, including the abandonment of the structure's grandiose base. Memorial stones for the interior were contributed by various states and numerous fraternal organizations. Pope Pius IX donated a stone from the Temple of Concord in Rome (though in 1854 members of the anti-Catholic Know-Nothing party broke into the obelisk, stole the marker, and disposed of it in the Potomac River). Construction was halted at the outbreak of the Civil War (American Civil War) with the obelisk standing only 152 feet (46 metres) tall. Mark Twain (Twain, Mark), who viewed the unfinished structure after the war, wrote that the monumenthas the aspect of a factory chimney with the top broken off…you can see cow-sheds about its base, and the contented sheep nibbling pebbles in the desert solitudes that surround it, and the tired pigs dozing in the holy calm of its protecting shadow.

After some preliminary discussion about tearing down the unfinished structure or changing its design, the Army Corps of Engineers assumed responsibility for its completion. Because it was impossible to find marble matching that used to construct the earlier portion, the colour of the upper two-thirds of the monument is visibly different from that of the lower third. Finally, some 36 years after construction began, the 3,300-pound (1,500 kg) capstone was set on the structure (December 6, 1884), and the Washington Monument was officially dedicated by President Chester Arthur (Arthur, Chester A.) during ceremonies on February 21, 1885. However, the monument was not opened to the public until October 9, 1888, following the installation of a steam elevator, which enabled visitors to reach the observation deck without walking up the monument's 897 steps. The modern elevator makes the ascent in about 60 seconds. Inserted in the interior walls are more than 190 carved stones presented by various individuals, cities, states, and foreign nations. After a major restoration project in the 1990s, the monument reopened in 2001.

Information on the Washington Monument and other important sites in Washington, D.C., can be found in a variety of sources, including Philip Bigler, Washington in Focus: The Photo History of the Nation's Capital (1988); Junior League of Washington, The City of Washington: An Illustrated History, ed. by Thomas Froncek (1977, reissued 1992); Charles Ewing, Yesterday's Washington, D.C. (1976); Constance McLaughlin Green, Washington, 2 vol. (1962–63; also published as Washington: A History of the Capitol, 1800–1950, 2 vol. in 1, 1976); Richard Longstreth (ed.), The Mall in Washington: 1791–1991 (1991); and Donald R. Kennon and Richard Striner, Washington Past and Present: A Guide to the Nation's Capital, 2nd ed. (1983, reissued 1993). Jim Berard, The Flying Cat and Other Amazing Stories of the Washington Monument (2000), is an informal account that provides anecdotes and statistics.B. Philip Bigler