Fort Ethan Allen was an earthwork fortification that the Union Army built in 1861 on the property of Gilbert Vanderwerken in Alexandria County (now Arlington County), Virginia, as part of the Civil War defenses of Washington (see Washington, D.C., in the American Civil War).

To allow for clear lines of sight toward other fortifications and approaches to Washington, D.C., the Army removed trees and other vegetation that were near the site.

[3] Built like other northern Virginia defenses, the fort was constructed following the directives of General John G. Barnard of the United States Army Corps of Engineers.

Cavalry garrison, one company (E) Thirteenth New York Cavalry–2 commissioned officers, 78 enlisted men, 53 equipped, 52 horses.

[1][3][9] In 2014, the Arlington County government installed nine interpretive panels within Fort Ethan Allen Park as part of its Neighborhood Conservation Program.

[10] In addition, the Virginia Civil War Trails[11] has placed a historic marker near the fort's site.

[3] An outlier trench, which the Arlington County Board has designated as a local historic district, remains to the southwest of the fort.