One of the many Civil War forts that did not disappear.
The Aqueduct Bridge is marked in red in both maps It is now named the Francis Scott Key bridge. The yellow bridge is named the Theodore Roosevelt bridge. The tan bridge is the Arlington Memorial bridge.
The blue dot on the left margin of the right map is where my office was with IBM in 1964.
It is the third location where my great grandfather and I were similarly located - Camden NJ, Richmond VA, and DC area.