The United States Capitol Dome may well be the most famous man-made landmark in America. It is such a fitting finale for the building it crowns, so familiar and dignified, that it seems surprising that its design and construction came late in the Capitol's architectural evolution. Only the West Front terraces (1884-1892), the East Front extension (1958-1962), and the Capitol Visitor Center are more recent additions to the Capitol than its dome (1855-1866). It was designed by the Philadelphia architect Thomas U. Walter, who was also the architect of the House and Senate extensions. Montgomery C. Meigs, a captain in the Army Corps of Engineers, was the principal superintendent of construction. Together they oversaw the creation of the Capitol's most memorable and remarkable feature.

The U.S. Capitol's first dome was finished in 1824 to the design of Charles Bulfinch, a Boston architect who was bringing the building to completion after more than 30 years of sporadic construction. Bulfinch's low dome was constructed of wood covered by copper. Light was admitted through an oculus. By the 1850s, this dome was considered too small for the vastly enlarged Capitol Building. It was also a fire hazard and was in constant need of repair. For these reasons, a new fireproof dome was considered a necessary and practical improvement to the Capitol.

On December 16, 1854, Walter hung in his office a drawing of the U.S. Capitol as it would appear once the extensions were finished, but without the Bulfinch dome. Instead the drawing showed a new cast-iron dome with columns, pilasters, brackets, scores of windows and a crowning statue. While it was only a suggestion of what a new dome might look like, the drawing caused an immediate sensation among Congressmen and Senators who visited the Architect's office. Within 10 weeks, without committee hearings and after little debate, the House of Representatives appropriated $100,000 to begin construction of a new Capitol dome. The Senate agreed a few days later, and President Franklin Pierce signed the legislation on March 3, 1855.