The Civil War Defenses of Washington (CWDW) were built by the Union Army between 1861-1864, to defend the nation’s capital against Confederate troops. Over the course of the war, the Army built up an extensive system of fortifications, capitalizing on the elevated hilltops that encircle the District of Columbia. For four years, the 37-mile ring of forts served as topographical, psychological, strategic, and military buffers to Confederate assaults on the capital, withstanding attack by Confederate General Jubal Early at the Battle of Fort Stevens in 1864.

By the war’s end in 1865, the defensive system included 68 enclosed forts, 20 miles of rifle trenches, and 30 miles of military roads. After the forts were dismantled and remitted to former owners after the war, efforts to preserve parts of the original fortification network met with varied success. The sites were included in the McMillan Plan of 1902, one of the earliest urban planning projects in the country focused on public recreation. The plan recommended reconnecting the sites through a combination of trails and scenic drives, resulting in a greenbelt around Washington. Although this plan was only partially realized, it did recognize and revive the forts' significance as a greenbelt around Washington, DC. In the 1930s, several of the forts were beautified, restored, or maintained by the Civilian Conservation Corps, a program of Franklin D. Roosevelt's New Deal.

Today, the National Park Service owns and manages 19 of the original fort sites. Researchers from the University of Pennsylvania have documented 7 of these parks for Cultural Landscape Inventories.