Fort Jackson, at the confluence of the Savannah and the Back rivers, was the site of a Revolutionary-period earthwork. The present fort was constructed between 1808 and 1812 as a Second System work and is noteworthy as an early all-masonry fort built by the United States. It initially consisted of a polygonal casemated work for six cannon facing the river, which was left open to the rear. The magazine, landside defensive works, and sally port were added in 1845–1861 but never completed. The traverse magazine on the terre plein (upper level) was added c. 1870. Fort Jackson was the hub of Civil War defenses of the Savannah River, with several waterside batteries constructed in the vicinity and the ironclad CSS Georgia moored directly across the channel. (The submerged remains of the Confederate ship are being salvaged as part of the ongoing project to deepen the Savannah River channel.) The ruins of the largest of these batteries, Fort Lee, are visible on the shore at low tide adjacent to the pier immediately downriver. The fort was restored by the State of Georgia during the 1960s and briefly opened as a maritime museum before the Coastal Heritage Society assumed site operations in 1975. The fort’s welcome center, the Tybee Depot (1888; 1990 moved and restored, Coastal Heritage Society), originally stood on President Street just east of downtown and served as the Savannah terminus of the railroad line connecting the city with Tybee Island from 1887 to 1933.