Smithsonian 'Castle' built of Seneca red sandstone

The Smithsonian Institution Building (the 'Castle') is constructed of red sandstone quarried at Seneca Quarry in Montgomery County, Maryland and was built in the mid-19th century. The material, commonly called Seneca red sandstone, gives the building its characteristic reddish appearance. Historical records note the stone's use and transport during the Castle's construction, and the quarry is documented in Smithsonian histories. The Castle remains a prominent example of the use of that regional sandstone in Washington architecture.