By 22 October, the first snowfall occurred. The river would soon freeze over. Then they reached the villages of the Mandan and Hidatsa nations. They had traveled 1,600 miles up the Missouri.
The Native Americans here were traders, and used to fur trappers, so they allowed Lewis and Clark to set up camp, spend the winter, and trade for food.
The expedition members raced against time to build a fort before the snows began in earnest. The fort was to be protection against the bitter Plains winter as well as any attack by the Sioux.
