What is left of Fort Johnson? Built in the early 1700s, the fort was expanded and improved during the French and Indian War, American Revolution, and War of 1812. During this same time the fort was damaged was hurricanes and storms. By the time of the Civil War only a few structures remained and Confederate forces built earthworks on the site. Today a circa 1820s brick powder magazine and a section Confederate earthworks are some of the surviving elements of the fort.