Smithsonian Institution Building, 1858, by Unknown, 1858, Smithsonian Archives - History Div, South facade of the Smithsonian Institution Building (SIB), the "Castle," after completion, c. 1858-1864, is dominated by a massive, square battlemented central tower with an attached octagonal stair tower rising well above it. Constructed in red sandstone quarried in Seneca, Maryland, the building was unique not only in style but in material. There is a fence around the building..