Fort Jackson is a decommissioned masonry fort located some up river from the mouth of the Mississippi River in Plaquemines Parish, Louisiana. It was constructed as a coastal defense of New Orleans between 1822 and 1832, and was a battle site in the American Civil War. It is a National Historic Landmark. It was damaged in Hurricanes Katrina and Rita and its condition is threatened. Following the engagement, Fort Jackson was used as a Union prison. It was here that the French Champagne magnate Charles Heidsieck was held for seven months on charges of spying.