Fort Union Trading Post was the most important fur trading post on the upper Missouri. Built in 1828 by the American Fur Company, the post was set up not as a government or military post, but as a business, established for the specific purpose of doing business with the northern plains tribes. This trade business continued until 1867 making it the longest lasting American fur trading post.At this post, the Assiniboine, Crow, Cree, Ojibway, Blackfeet, Hidatsa, and other tribes traded buffalo robes and furs for trade goods including items such as beads, clay pipes, guns, blankets, knives, cookware, cloth, and alcohol. Lots of alcohol. Historic visitors to the fort included John James Audubon, George Catlin, Pierre DeSmet, Sitting Bull, Karl Bodmer, and Jim Bridger.It was declared a National Historic Landmark in 1961.