The US Capitol is among the most architecturally impressive and symbolically important buildings in the world. It has housed the meeting chambers of the Senate and the House of Representatives for two centuries, and is part of the Capitol Complex, which includes six Congressional office buildings and three Library of Congress buildings. It is not only the focal point of the Legislative Branch of government, but is also a museum of American art and history, and is visited by an estimated 3-5 million people per year.
The 19th-century neoclassical architecture of the Capitol was derived from ancient Greece and Rome, and as the building was expanded from its original design (by Dr. William Thornton in 1792), harmony with the existing portions was maintained. At 751 feet long and 350 feet wide, its floor area is approximately 16-1/2 acres. The building contains approximately 540 rooms, 658 windows (108 in the dome alone) and approximately 850 doorways.