Fort Crawford in Prairie du Chien, Wisconsin, was a major United States Army post on the upper Mississippi frontier, maintained in two successive forts from 1816 to 1856. Built first after the War of 1812 and later rebuilt in limestone on higher ground, it served as part of a wider military network and as a center of diplomacy, including the 1825 Treaty of Prairie du Chien council. It was also linked to the Black Hawk War, William Beaumont’s medical experiments, the military road to Fort Winnebago, and the presence of slavery despite legal prohibitions. The site later held a Civil War hospital, and its reconstructed hospital survives as a National Historic Landmark.