When South Carolina seceded from the Union in December of 1860, Union forces in the area took refuge in Fort Sumter, in Charleston Harbor. But after being holed up for awhile, the Union troops started running out supplies. Ready to demand their surrender, Confederate forces fired on Fort Sumter on April 12, 1861—exactly 155 years ago. The shots touched off a battle that would last for days and a war that would last for years, threatening the very future of the United States.
Though the attack claimed no soldiers' lives in the time before the Union forces surrendered Fort Sumter, it would live in history as the battle that formally began the Civil War. And, as these photographs show, it left its physical mark on the building.
The Civil War is famous for its relationship with photography, falling at a time of rapid advancement in camera technology. Though the film we might rec0gnize today had yet to be invented, photographers were experimenting with gadgets like the stereograph—an early 3D-photo technology, seen in the images above, where two photos from slightly different angles are viewed through a device that makes the human eye see them as one deep image. They were also experimenting with the possible uses of photography for spreading the word about what was going on in the nation. As the Civil War raged on, photographs communicated its horrors to Americans far from the battle fields, in a way that the art of previous wars had not made possible.
Read TIME's 2011 cover story on the 150th anniversary of the Fort Sumter attack, here in the TIME Vault: Why We're Still Fighting the Civil War