The U.S. Capitol is a unique structure, as it has been built in successive phases over the past two centuries. The estimated historical cost of the United States Capitol as of 2003 was $133 million. This includes the original building (the Rotunda and the north and south wings) as it stood in 1824 ($2.4 million), the cast-iron dome added in 1866 ($1 million), and the extensions (which house the present House and Senate chambers as well as office and support spaces) completed in 1867 ($8.1 million).
Numerous additions, renovations and modernization efforts made throughout the years added another $122 million. Improvements to the Capitol Grounds have an estimated historical cost of $33.8 million as of fiscal year 2003; these include such items as landscaping, sidewalks, and security features. This estimate does not include the addition of the newest addition to the Capitol, the Capitol Visitor Center, which was constructed after 2003.
Note that these numbers are given in historical dollars spent and have not been inflated to reflect current-day replacement value.