The first forts to appear on the plains were not built for military
purposes but for trading. The drawing above depicts Fort Pierre, which was
built in the Dakota Territory in 1831. The painted signs over the gate
invite Indians (in this case Teton Sioux) to exchange buffalo hides for
guns, cooking utensils, and other trade goods. The early Plains forts also
served as "neutral territory" where warring tribes could meet for trade.
In the 1850's, the U.S. Army began building military forts on the plains
to protect emigrants to California and Oregon. In 1855, Fort Pierre's
owner, Pierre Chouteau, sold it to the U.S. government for use as a
military post.