Fort Berthold was the name of two successive forts on the upper Missouri River in present-day central-northwest North Dakota. Both were initially established as fur trading posts. The second was adapted as a post for the U.S. Army. After the Army left the area, having subdued Native Americans, the fort was used by the US as the Indian Agency for the regional Arikara, Hidatsa, and Mandan Affiliated Tribes and their reservation.
In the mid-1950s both of the former fort sites were submerged under Lake Sakakawea, created by extensive flooding of the bottomlands after the Garrison Dam was constructed on the Missouri River.
The forts were named after Italian-born Bartholomew Berthold (1780–1831),[1] a prominent merchant and fur trader of St. Louis. He collaborated with the Chouteau and Astor families in trading in this region.
He built what became known as the Berthold Mansion at Fifth (now Broadway) and Pine streets in St. Louis. Decades after his death, it was used as the headquarters of the Democratic Party. After Abraham Lincoln's election in 1860, the Berthold mansion was used for pro-Southern secessionists known as Minute Men. It was then known as "Fort Berthold".[2]