The Washington Building is a landmark in Washington, D.C. and is commonly referred to as the Capitol. It is the home of the United States Congress and is the seat of the legislative branch of the federal government. The building was designed by William Thornton and completed in 1800. It has been expanded and renovated several times since then, most recently in 1958. It is a National Historic Landmark and is one of the most recognizable symbols of the United States.