Saltpeter Cave, carved out of nearby limestone by thousands of years of stream erosion, supplied ingredients used by American soldiers for decades because muskets could not fire without gunpowder. After nitrates were discovered in the cave, Thomas Jefferson decided to lease it for the production of saltpeter, a major ingredient in early gunpowder. Saltpeter made at this site was used in the War of 1812 and the Civil War. Although nitrate-rich compounds in many caves came from the droppings of bats and birds, research has shown that in the southeastern United States these compounds originate from a complex process of nitrogen-fixing bacteria, oxidation, and evaporation. The compounds were collected from the cave and then boiled to concentrate and crystalize the potassium nitrate into saltpeter.