In 1860 the fort was about 90% complete when work stopped after South Carolina seceded from the Union. In the early hours of April 12, 1861, a mortar shell exploded over the fort starting the Civil War. During the war, Fort Sumter remained in Confederate hands. From 1863 to 1865 Union forces laid siege to the fort. For 587 days Confederate soldiers held onto the fort, although by 1865 the fort had been completely destroyed by Union bombardments.