Famous Roofs: Dome of the United States Capitol


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A dome that’s 288 feet high and 96 feet across sits above the United States Capitol’s rotunda. This dome is one of the most famous roofs in the entire world. The dome also has a long history that stretches all the way back to America’s first president, George Washington. It appears to be made of stone, but it’s actually made of cast iron painted to match the stone of the rest of the building. It’s also not just one dome: It’s actually two, one inside of the other. The iron was cast by Janes, Fowler, Kirtland & Company, a Bronx foundry.

First Dome

George Washington asked Thomas Jefferson, then the secretary of state, to sponsor a design contest for a new capitol building in 1792. Dr. William Thornton won the contest, and he included a dome in his design. Thornton was influenced by the roof of the Roman Pantheon. The second architect of the Capitol, Benjamin Henry Latrobe, changed Thornton’s design to more clearly visually divide the sides of the building from the bottom of the dome. Charles Bulfinch, the next architect, increased the height of the dome. In 1822, President James Monroe approved $120,000 in funding that was supposed to pay for a structure consisting of two nested domes. The interior dome would be made of brick, wood, and stone and rise 96 feet above the floor of the rotunda. These dimensions match those of the Pantheon. An exterior dome was to be constructed of wood and covered with copper. Bulfinch finished the work in 1823. Until the 1850s, the copper dome of the Capitol dominated views of the city. But as the country grew, so did Congress, until it got too big and needed more space. Larger wings were built onto the building, but the wings threw off the proportions of the dome. Congress then passed legislation in 1855 to rebuild the dome.

Second Dome

Plans for the current dome, made of cast iron, began in May 1854. The dome was to be more beautiful than the first and also be fireproof. The new dome was inspired by the Pantheon of Paris and Saint Isaac’s Cathedral in St. Petersburg, Russia. Architect Thomas Walter created a seven-foot drawing of his design to win the approval of Congress. President Franklin Pierce approved $100,000 in funding (which is about $2.2 million in today’s dollars) to build the new dome. Some functional changes were made to the original design, and construction began by removing the original dome. The steam-powered crane used to construct the new dome was powered by burning the wood from the original dome.

Construction of the dome, which like the original consisted of an interior and exterior dome, took 11 years. In December 1863, the Statue of Freedom was placed on top of the dome. The statue required the design of the dome to be revised during construction because it was made taller and more substantial than specified by the architects. Work was officially completed in January 1866 when Constantino Brumidi finished The Apotheosis of Washington, a fresco on the interior dome. The construction project used 8,909,200 pounds of iron. The interior dome reaches 180 feet above the floor of the building, and the exterior dome is 288 feet up. It cost $1,047,291, which is the equivalent of about $14.5 million today.

The Dome Today

Only members of Congress and those they invite to come along are allowed to tour the dome. The railing that protects visitors to the dome is barely visible when looking up at the dome from the rotunda floor. There’s also a set of metal stairs between the interior and exterior domes, which eventually lead visitors to a walkway directly below The Apotheosis of Washington. Another set of stairs takes visitors to an outside balcony underneath the Statue of Freedom. Directly under the statue is a small room containing lights that are lit when one or both chambers host a night session.

A major renovation project was undertaken starting in 2013. The project cost about $10 million. The dome needed both interior and exterior work; the ironwork was in particular need of attention. The project was finished in 2016.

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