Powder Magazine was built in 1713 to store gunpowder

The colonial assembly authorized a gunpowder storehouse in 1703, and it took ten years to build. Finished in 1713, this twenty-seven-foot square brick room is the oldest public building in the Carolinas, and the oldest surviving building across both colonies put up for a purpose other than worship. It is also the only public building remaining from the rule of the Lords Proprietors, the eight English aristocrats who owned Carolina between 1670 and 1719.

Charles Town was the southernmost English settlement on the continent, walled, moated, and repeatedly attacked by Spanish naval vessels, pirates, and Native nations. The assembly put the storehouse just inside the northern wall of the town, away from most of the houses, to hold the gunpowder needed for defense.

The structure was engineered to direct an explosion straight up. The brick walls measure nearly three feet thick at the base and taper as they rise, thinning to a few inches at the top of the vaulted roof. If the stored gunpowder ignited, the blast would blow out the thin roof rather than breach the walls into the surrounding streets. Tons of sand stored in the attic above the vault were intended to blow upward with the roof and fall back down onto the flames to smother the fire.

The military largely abandoned the magazine after the American Revolution, stored powder in it briefly in 1820, and decommissioned it in 1821. Because the thick walls remained solid, later owners adapted it into a print shop, a stable, and a carriage house, using the interior to store Madeira wine, art, and silver plate. The National Society of the Colonial Dames in South Carolina purchased the building in 1902 to stop its demolition and turned it into a museum. It became a National Historic Landmark in 1989, and the Historic Charleston Foundation leased and restored it in 1993 to its mid-nineteenth-century appearance.