On April 18, 1861, the day following Virginia's secession, several companies of state militia closed in on the 47 army regulars defending the arsenal. The Union soldiers set fire to the buildings and fled. The Virginians reacted quickly and saved most of the machinery. For a time, Harpers Ferry was the northernmost point of the Southern Confederacy.
Source: Robertson, Jr., James I. "Harpers Ferry Civil War Campaign." e-WV: The West Virginia Encyclopedia. 17 February 2012.