At this site on Salter's Island on the east side of Savannah, a small earthwork called Mud Fort was built in 1776 but was soon abandoned because of unhealthy conditions. In the early 1800s, President Thomas Jefferson authorized coastal fortifications, and this location was chosen for a new brick fort named Fort James Jackson after a local Revolutionary War hero who later became a U.S. Senator and Governor of Georgia. Work began in 1808, and within four years the waterfront brick battery was completed; construction continued between 1847 and 1861, and by the beginning of the Civil War the fort had become a formidable stronghold. On Saturday, January 26, 1861, Georgia militia under Colonel Alexander R. Lawton seized the fort. Although it was never heavily engaged during the Civil War, it served as headquarters for the Confederacy's Savannah River defenses, with local units including the Irish Jasper Greens, Republican Blues, 1st Georgia Regulars, and 22nd Georgia Heavy Artillery Regiments in garrison. The Confederacy built earthen fortifications around the fort and along the river, some supervised by General Robert E. Lee, placed numerous cannon in them, and used floating and submerged explosives and other obstructions in the water to block Federal ships moving upstream toward the city. Extra protection came from the Confederacy's Savannah River Squadron of seven gunboats and four ironclad ships. By December 1864, as Union Major General William T. Sherman's army approached Savannah, Confederate troops evacuated the city on Tuesday, December 20th. The garrison at Fort Jackson burned the barracks, threw weapons and ammunition into the moat and river, spiked the guns, booby-trapped the powder magazine, and scuttled the ironclad Georgia in the river in front of the fort. The next morning the Federal 28th Pennsylvania and 29th Ohio Infantry Regiments arrived to find the fort abandoned and still burning, and members of the 29th Ohio climbed the ramparts to raise the Stars and Stripes. The last unit stationed there during the war was the Federal 55th Massachusetts, an African-American infantry regiment.