Fort or Camp Lyon in Alexandria, Virginia was rocked by an explosion on June 9th 1863 that killed 21 Union soldiers.
Fort Lyon was constructed just south of Alexandria, Virginia, named for Union Brigadier General Nathaniel Lyon. It was a timber and earthworks fort, built in the weeks after the Union defeat at First Bull Run. Union General Samuel P Heintzelman was the commander of Fort Lyon from October 27th 1862 to October 13th 1863, and was in charge of the defense of Washington, DC.
The fort was shook by a massive explosion of black powder on June 9th 1863. Men from the 3rd New York Artillery were refilling shells with powder, when a spark from one of the cast iron shell cases caused the explosion. It destroyed some eight tons of black powder, and a couple thousand rounds of ammo, as well as killing 21 Union soldiers and wounding another 10. One witness to the explosion described it as “a most violent thundering explosion, followed by another, in quick succession, the earth shook and trembled... I was so frightened...a shell burst very near, for a little stream of blue smoke came in one door and passed out the other... I looked up at Fort Lyon, which at that moment went up with a tremendous shock.”
Following the blast many civilian, military and political leaders, including President Abraham Lincoln visited the site.