What an awesome photograph from the Civil War. This shows a haymarket, with (what I believe to be) the Smithsonian in the background. If I’m mistaken, please let me know what those buildings are.
Source: Library of Congress
An Awesome Photograph from the Civil War: A Haymarket in Washington, DC
Great pic! Check out http://www.si.edu/oahp/sibtour/ to see various pictures of the inside of the castle – some from around the same time period.
You’re right that that is the Smithsonian Castle behind the market and even better, the photo shows the damage to the building from its 1865 fire!