General Thomas swearing in the volunteers called into the service of the United States at Washington, D.C.

The Architect of the Capitol (AOC) is the federal agency responsible for the maintenance, operation, development, and preservation of the United States Capitol Complex, which includes the U.S. Capitol building, the Library of Congress, the Supreme Court, and the House and Senate office buildings. It was established in 1855 and is one of the oldest federal agencies in the United States. The AOC is responsible for the maintenance and upkeep of the buildings and grounds of the Capitol Complex, as well as the preservation of the historic and artistic elements of the buildings.