“Section through Dome of U.S. Capitol,” by Thomas U. Walter, 1859

In addition to being architect of the Capitol extension, Walter was also the architect of the new cast-iron dome. This drawing illustrates how the architect fit the new iron structure on top of the old rotunda walls. A lower ring of columns, supported on brackets cantilevered from the rotunda walls, allowed the new dome to surpass the diameter of the old dome by 30 feet and thus appear more appropriate for the newly expanded building.  A smaller, inner dome complemented the proportions of the existing rotunda.

Architect of the Capitol