On Christmas Eve 1851, the Library of Congress was gutted by a disastrous fire. Before the ashes had cooled Thomas U. Walter, the architect of the Capitol extension, was asked to supervise its reconstruction. In response, Walter designed the first room in America with an iron ceiling. The book cases and balconies were also cast iron, an inexpensive, quickly made, and, most importantly, fireproof material. The innovative room was completed in 1853 and used for four decades before being dismantled in 1900, three years after the library moved to its own building in 1897.
Prints and Photographs Division, Library of Congress