One never knows what one will find if you rummage around the United States' attic...
Driving around the "DMV" - District, Maryland & Virginia - one will often see signs of the US Civil War - National Park Service signs that announce a fort such as Fort Davis or Fort Foote or Fort Totten with little but a few earthworks mounds to see and hardly any sign of what was there over 150 years ago. Yet by the end of the war, there would be 68 forts along with some 90 artillery batteries that would be the defense of the perimeter of the Capital City of Washington DC. Major General John G. Barnard was the engineer who designed most of these fortifications. He is often called the "Father of the Defenses of Washington DC".
Today, only a few of those fortifications and artillery batteries still exist in more than just those signs and mounds of earth - Fort Stevens in Washington DC and Fort Ward in Alexandria, Virginia are two that have been conserved in entirety or partially to show part of the Defenses of Washington DC.
National Park Service Presents a Tour
It was 1938, the 75th anniversary of the battle of Gettysburg during the US Civil War. It was when the Civil War was something fresh in the minds of the people who experienced it, the National Park Service provided a tour of "the Defenses of Washington DC" From that tour here is a twenty page booklet that was provided to those who took the tour. (Be patient - the book may take a bit to load)