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United States Capitol
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Vital Statistics:
Location: Washington, D.C., USA
Completion Date: 1824
Cost: $1 million
Diameter: 96 feet
Type: Ribbed
Purpose: Political
Materials: Cast iron
Engineer(s): Montgomery C. Meigs, William B. Franklin

One of the first great domes to crown a wholly political building, the United States Capitol dome in Washington, D.C. has had quite an eventful history. Since George Washington laid the cornerstone in 1793, the Capitol has been built, burnt, rebuilt, extended, and restored.

United States Capitol
Click photo
for larger image.

The Capitol's first dome was completed in 1824 to the design of Boston architect Charles Bulfinch -- and it was a profound disappointment. Aside from its appearance, which no one liked, the dome was a fire hazard and in constant need of repair. In 1855, Philadelphia architect Thomas U. Walter was ordered to replace the old dome with a bigger, better, fireproof dome.

A taller, heavier dome whose walls would not crack or push outwards would require massive walls like the Pantheon or lots of iron chains like St. Peter's Basilica. But Walter didn't want that. So he designed a double dome -- a small dome inside a taller dome -- that created the illusion of height. The tall exterior dome is really a thin shell, supported by a ring of 36 curved iron ribs. Underneath is a smaller dome, open at the top like the Pantheon. Though it looks like it's made of stone, every bit of the Capitol dome is made of cast iron.

The dome was finally completed in December 1863, and it stands today as the consummate symbol of American democracy.

Here's how this dome stacks up against some of the biggest domes in the world.
(diameter, in feet)

Chart showing the relative size of the biggest domes in the world United States Capitol
96'

Fast Facts:
  • The United States Capitol building contains approximately 540 rooms and has 658 windows (108 in the dome alone) and approximately 850 doorways.
  • The dome was constructed with 8,909,200 pounds of iron.
  • The bronze Statue of Freedom is the crowning feature of the dome of the United States Capitol. It stands 19 feet 6 inches tall and weighs approximately 15,000 pounds.

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