The Treasury Building is the oldest departmental building in Washington and has had a great impact on the design of other governmental buildings. At the time of its completion, it was one of the largest office buildings in the world. It served as a barracks for soldiers during the Civil War and as the temporary White House for President Andrew Johnson following the assassination of President Lincoln in 1865. The Treasury Building is unquestionably a monument of continuing architectural and historical significance. In acknowledgment of the building’s significance, it was declared a National Historic Landmark in 1972.