Fort Sully was one of the main military posts located on the east bank of the Missouri river in central Dakota built for use in the Indian Wars. There were two forts named Sully—old Fort Sully, which was in existence and occupied from 1863 to 1866, and the later, or new Fort Sully, which was established in 1866 and was continuously occupied as a military fort until its abandonment in the fall of 1894.