What Union Occupied estate near Fort Craig overlooks the Potomac River ?
Fort Craig (Virginia):  Fort Craig stood less than a mile away from Arlington House, the Union-occupied estate of Confederate General Robert E. Lee. Arlington House, The Robert E. Lee Memorial:  It overlooks the Potomac River and the National Mall in Washington, D.C. During the American Civil War, the grounds of the mansion were selected as the site of Arlington National Cemetery, in part to ensure that Lee would never again be able to return to his home.
Arlington House