L'Enfant regarded the Capitol building the central focus of the design of the Federal City. He placed the Capitol on the west end of Jenkin's Hill which he described as " a pedestal waiting for a monument." He felt that public buildings should be placed on hills so that they held commanding views. Axial vistas with reciprocal views were a basic part of his planning philosophy. The Capitol grounds were redesigned by Frederick Law Olmsted in 1874 in the naturalistic tradition with serpentine paths and heavy foliage. In 1897 the Library of Congress was constructed, and no further development took place until the Senate Park Commission Plan of 1902. The Senate and House office buildings and the Supreme Court were constructed in accordance with grand plan for the Beaux Arts inspired buildings to serve the needs of the legislative and judicial arms of government.
In 1791, George Washington and L'Enfant settled on the location of the "President's Palace," on a high ridge with views extending down to the Potomac. It provided an answering vista to the Capitol at the end of Pennsylvania Avenue, a great diagonal avenue linking the two buildings. To the south, the Washington Monument is located off-axis, and to the north is Sixteenth Street beginning at the edge of Lafayette Square. The White House grounds to the south, the ellipse, contains major sculptural memorials from the nineteenth and twentieth centuries. L'Enfant designed 16th St to have the same width as the large diagonal avenues and Lafayette Square in front of the North fašade of the White House terminates the 16th Street axis. The design of Lafayette Park was not in place until 1824, and the present landscape plan dates from the 1930s.
Between 1798 and 1800 two executive office buildings, the Treasury Department and the War Office, were constructed adjacent to White House. The new Treasury building was begun in 1836, and work continued for three decades. The placement of the Treasury building on this site effectively blocks the vista between the Capitol and the White House. The present Old Executive Office Building that was formerly the State, War, and Navy Building was built between 1871 and 1888.
Jefferson's original conception of the capital was to provide a "public walk" in the center of the city which linked the Capitol Building and the White House. L'Enfant had provided for an avenue lined with great residences, but his plan was forgotten in the intervening years. Andrew Jackson Downing provided for a curvilinear plan in 1851. And the Mall we see today is the result of the McMillan Plan lined with museums and the Department of Agriculture.
The Old Patent Office (7th, 9th, F and G Streets, NW) which now houses two Smithsonian Museums, the National Museum of American Art and the National Portrait Gallery was built between 1836 and 1857(Open to the public, but soon to be closed for major renovations). This site is outside the monumental core, and sits on the same high ridge as does the White House and had been noted on L'Enfant's plan as a place for a nondenominational church dedicated to America's heroes. The Patent Office was perceived as a fitting substitute, and the Smithsonian Museums have carried on that tradition. The United States Tariff Commission Building (United States General Post Office) at 8th and F Streets, is another grand public building in this same area and plans are currently underway to redevelop the property.
The Federal Triangle is located on a triangular site bounded by Pennsylvania Avenue, Constitution Avenue, and 15th Street. Ten structures designed by different architects are located on the site. Two of the structures, the Old Post Office and the District Building, were constructed between 1899-1908. The rest were constructed between 1926 and the 1930s except for the Ronald Reagan Building and International Trade Center which was designed and constructed in the 1990s. The planning for the Federal Triangle was one of the last City Beautiful efforts on such a monumental scale in the nation. The triangle achieves a harmony of scale and proportion through the use of similar materials and an elaborate landscape plan.
From the time of the McMillan Commission Plan the area to the west of the ellipse was planned for monumental buildings which would enframe the newly extended Mall. By the 1930s, the growing expansion of the Federal government led to the conception of a formal plan for a monumental complex of Federal buildings to balance the Federal Triangle on the east side of the ellipse.
This new area was called the "Northwest Rectangle" and soon saw a large complement of Federal buildings such as the Public Health Service (1931-33), the New Interior Department (1936) and the Federal Reserve (1937). The grand plan for the Northwest Rectangle was never completed. Later government buildings in the area, the Department of State (1957-60), the Civil Service Commission (1960s) and the Federal Reserve Annex (1970s) reflect modernist rather than classical design. After World War II, there was much more decentralization of Federal agencies, many of which are now located in the regional areas of Maryland and Virginia.