United States Capitol dome

The United States Capitol dome is the dome situated above the United States Capitol which reaches upwards to 288 feet (88 m) in height and 96 feet (29 m) in diameter. The dome was designed by Thomas U. Walter, the fourth Architect of the Capitol, and constructed between 1855 and 1866 at a cost of $1,047,291 (equivalent to $232 million in 2015). The dome is not stone, but cast iron carefully painted to appear to be made of the same stone as the main capitol building. It is actually two domes, one inside the other, and the total weight is 14.1 million pounds (6,400 t). The iron for the dome was cast by the foundry of Janes, Fowler, Kirtland & Company, owned by Adrian Janes in the Bronx, New York.

The origin of the first dome began with the Capitol design contest sponsored by Secretary of State Thomas Jefferson, at the behest of President George Washington, in 1792. The winner of the contest, Doctor William Thornton, called for a dome in his original design for the building. Most vividly, Thornton drew upon the Roman Pantheon for inspiration with the Neoclassical dome and associated portico.

Thornton's replacement, Benjamin Henry Latrobe, the second Architect of the Capitol, altered Thornton's design plan on the exterior by adding an octagonal drum to visually separate the bottom of the dome from the top of the building's pediment. The third Architect of the Capitol, Charles Bulfinch, altered the exterior profile of the plans still further by increasing the dome's height, which he later wrote was at the insistence of the President and Congress.

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