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Prewar Fort SumterOn April 12, 1861—150 years ago today—Confederate artillery fired the first shots of the U.S. Civil War on Fort Sumter, a Federal stronghold at the mouth of Charleston Harbor (map) in South Carolina.(Read "Fort Sumter: How Civil War Began With a Bloodless Battle.") With the election of Abraham Lincoln five months earlier, the long-simmering threat of disunion had finally swept across the United States. Powerful political forces in the Southern states chose to end the compromises that had held the Union together since its creation. South Carolina left first, following through on its promise to leave should Lincoln be elected president.After South Carolina’s secession in December 1860, a Federal garrison moved to take control of Fort Sumter. Four months later, the Union would surrender the fort after a 34-hour battle with the surrounding Confederates.The modestly fanciful Currier & Ives print above shows Fort Sumter in its peaceful, pre-war setting, positioned atop a man-made granite block island in the middle of the main entrance to Charleston Harbor. The fort served as the centerpiece of the defenses of the city’s seaward approaches.Construction of the five-sided brick and masonry fort began in 1827 but remained partially incomplete when battle broke out in 1861. (Read "Civil War Battlefields" in National Geographic magazine.)Between 1827 and 1861, advances in heavy artillery firepower had nearly rendered the fort’s five-foot thick walls obsolete. By the time of the Civil War, the size and velocity of guns carried on warships had increased dramatically.This might be fairly judged as just another mismatch wrought by the Industrial Age’s arms race, but something the fort’s designers could not have foreseen was a threat from even heavier land-based guns firing from neighboring fortifications. Indeed, no military engineer could have anticipated that the other forts in the Charleston defenses would fall into hostile hands and take aim at Fort Sumter. No plans had anticipated South Carolina’s secession.Despite this fateful miscalculation, Fort Sumter’s massive bulk would soon demonstrate a remarkable ability to take punishment. Even when reduced largely to rubble, the fort could still protect its garrison and support a handful of gun batteries that were sufficient to fend off attackers.MORE FORT SUMTER AND CIVIL WAR COVERAGE