Fort Ethan Allen was an earthwork fortification built on the property of Gilbert Vanderwerken in Alexandria County, Virginia, (now Arlington, Virginia) by the Union Army in 1861 as part of the defense of Washington during the American Civil War. The remains of the fort, a portion of the earthen walls, now overgrown, are now part of Fort Ethan Allen Park. It was listed on the National Register of Historic Places in 2004. It is designated as an Historic District by Arlington County, and is included as a site in the Virginia Civil War Trails program.