The United States Capitol features a dome situated above its rotunda. The dome is in height and in diameter. Designed by Thomas U. Walter, the fourth Architect of the Capitol, it was constructed between 1855 and 1866 at a cost of $1,047,291 (equivalent to $ in ). The dome is not stone, but rather 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 . The dome's cast iron frame was supplied and constructed by the iron foundry Janes, Fowler, Kirtland & Co. in the Bronx, New York. The dome marks the origin on street maps of Washington, D.C. A detailed look at the dome and its recent restoration can be found here. First dome 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. In 1822, Bulfinch requested funds for the construction of the center of the building, and President James Monroe signed off on an appropriation of $120,000. This included the building of a double-dome structure, a stone, brick, and wooden interior dome to rise above the rotunda floor (matching the dimensions of the Pantheon), and a wooden exterior dome covered in copper that would rise to . Set at the crown of the exterior dome was an oculus wide, which provided illumination to the rotunda floor below. Bulfinch completed the project in 1823. For more than two decades, the green copper dome of the Capitol greeted visitors to the nation's capitol, until the 1850s. Due to the growth of the United States and the expansion and addition of