Fort Slocum Park

Fort Slocum was one of seven temporary earthwork forts, part of the Civil War Defenses of Washington, D.C., during the Civil War, built in the Northeast quadrant of the city after the beginning of the war by the Union Army to protect the city from the Confederate Army. From west to east, the forts were as follow: Fort Slocum, Fort Totten, Fort Slemmer, Fort Bunker Hill, Fort Saratoga, Fort Thayer and Fort Lincoln.

Source: Wikipedia