Photo courtesy of Library of Congress.

Ever walked from the Foggy Bottom Metro stop down to the Mall? You’ve likely walked down 23rd Street and noticed a highly fortified complex near E Street, owned by the Navy. what you’re walking by is the Potomac Annex, also known as the Old Naval Observatory.

Located on Reservation 4 of the L’Enfant Plan for the Federal City, George Washington chose the site for a university, but it was never built. It has been occupied by the Navy since 1842, and the United States Naval Observatory was built there in 1844. A 13-acre site, it has numerous historic structures beyond the Old Naval Observatory, including the old Washington Naval Hospital and the Naval Medical School. Also on the site is a statue of Benjamin Rush, a signer of the Declaration of Independence and professor of medical theory and clinical practice as well as archaeological remains associated with the 1844 magnetic observatory and tunnel.

It is believed that in 1755, during the French and Indian War, that General Braddock’s troops may have camped nearby, and a burial ground for those who died during an epidemic that same year could be located on the western slope of the Potomac Annex.

Although the site is nationally significant, the site itself is not protected by either the National Register of Historic Places or National Historic Landmark. The old Naval Observatory, currently known as Building 2 of Potomac Annex, however is listed on the National Register of Historic Places and is a National Historic Landmark. D.C. Preservation League put the site on its 2007 Most Endangered Places List as there were some concerns about how the Federal government might develop the property. The Preservation League often offers tours of the site for a small fee.