Fort Johnson/Powder Magazine is a historic gunpowder magazine located at James Island, Charleston County, South Carolina. It was built in 1765, and is a brick structure that measures 27 feet long and 20 feet wide. Fort Johnson was constructed by the British, 1704-1708, and was named for Sir Nathaniel Johnson, proprietary Governor of the Province of Carolina. This was the site of the first raising of the South Carolina state flag in 1775. The gunpowder magazine was buried during the American Civil War by Confederate soldiers and uncovered in 1961.