Fort Lyon (usually Camp Lyon in Northern records) was a timber and earthwork fortification constructed south of Alexandria, Virginia as part of the defenses of Washington, D.C. during the American Civil War. Built in the weeks following the Union defeat at Bull Run, Fort Lyon was situated on Ballenger's Hill south of Hunting Creek, and Cameron Run (which feeds into it), near Mount Eagle. From its position on one of the highest points south of Alexandria, the fort overlooked Telegraph Road, the Columbia Turnpike, the Orange and Alexandria Railroad, the Little River Turnpike, and the southern approaches to the city of Alexandria, the largest settlement in Union-occupied Northern Virginia.