United States Capitol Complex, Government complex in Washington, D.C., United States

The United States Capitol Complex is a group of government buildings in Washington, D.C., spreading across roughly 100 acres and encompassing several key structures. It includes the main Capitol building, offices for senators and representatives, the Library of Congress, and the Supreme Court.

Construction of the Capitol began in 1792, and the building was designed to house not only Congress but also the Library of Congress, the Supreme Court and the district courts. The Capitol and its grounds were enlarged as Congress grew, reaching essentially their present size and appearance by 1892, apart from the east front extension of 1958–1962 and courtyard infill of 1991–1993. The Capitol Complex took shape once the Library of Congress moved into its own building in 1897 and separate House and Senate office buildings followed in the early 20th century.

The Capitol Rotunda displays significant American artworks including historical paintings and sculptures representing different periods of national development. Visitors can also explore the ornately decorated Brumidi Corridors with their intricate frescoes and detailed decorative elements.

The Capitol Visitor Center, opened in December 2008 at a cost of $584 million, holds an exhibition gallery, two theaters, a dining facility and gift shops. All House and Senate office buildings except the Ford and O'Neill buildings link to the Capitol through underground tunnels or people movers, so staff and visitors can move between them without going outside.

The dome is made of cast iron and weighs around 4 million kilograms, making it one of the heaviest dome roofs in the world. This structure was an engineering feat at the time, as it was built entirely from metal to support the immense weight.