The Washington Monument, a large white-colored obelisk at the west end of the National Mall, is constructed of marble, granite and sandstone and was built as a memorial for George Washington. Designed by Robert Mills, construction began in 1848, but not completed until 1884, 30 years after Mill's death, resulting from lack of funding and the Civil War. A difference in shading (visible at 150 feet) delineates the two phases of construction. Its cornerstone was laid on July 4, 1848; the capstone was set on December 6, 1884, and the completed monument was dedicated on February 21, 1885. It officially opened to the public on October 9, 1888. At the time of its completion it became the world's tallest structure at 555 ft 51/8 in, a title it inherited from the Cologne Cathedral and held until 1889, when the Eiffel Tower was finished in Paris. It is still the tallest structure in DC and due to a 1910 law restricting new building's height from being no more than 20 feet greater than the width of the street they're on, probably always will be.
Despite momentum for an appropriate memorial in the new capital following Washington's death, progress was finally made in 1833--the centennial of his birth. The Washington Monument Society began collecting donations and announced a design competition in 1836. Mills, who had designed the Washington Monument in Baltimore, was selected with a design that called for a 600-foot obelisk, topped by Washington in a chariot, and surrounded with a circular colonnade, but an exorbitant price tag of $1M.
In 1849, after 4 years of non construction, to combat escalating costs after 4 years the Society encouraged states and territories to donate memorial stones, which came pouring in from all sorts of organizations, businesses and foreign nations, often bearing inscriptions with no relevance to Washington. After the anti-Catholic, nativist Know-Nothing's stole a block donated by Pope Pius IX and took control of the Society in an election many claimed to be fraudulent, Congress rescinded the $200k contribution they had promised. The Know-Nothing's eventually ceded control in 1858.
It wasn't until after the Civil War, in 1876, that the Congress appropriated another $200k to complete the monument. After renewed conversation around design, the Society abandoned Mills' colonnade and altered the obelisk to conform to Egyptian proportions. Construction resumed in 1879 under Lieutenant Colonel Thomas Lincoln Casey and was completed within 4 years.
In 2007, The Washington Monument was ranked #12 on the AIA 150 America's Favorite Architecture list.