Situated on a small man-made island in the bay, guarding the entrance to Charleston Harbour, Fort Sumter National Monument is one of the most important historic military sites in the country. It was built using 70,000 tons of granite and rock, simply dumped into the water to form a man-made island. The rock and granite had to be brought in from as far afield as new York City. The first shots of the American Civil War were fired at Fort Sumter in 1861. With the secession of South Carolina, the Confederates demanded the surrender of the fort, and after 34 hours of continuous bombardment the Union forces had no choice but to relinquish their hold. The Union troops became the first prisoners of the Civil War. The Confederates occupied Fort Sumter, which became a symbol of Southern resistance until it was retaken by Union forces in 1865 after nearly four years of almost continual attack, which reduced most of the fort to rubble. Park rangers conduct free tours around the restored structure, which includes a museum with historical displays.