Fort Benton was the eastern terminus of the Mullan Military Road. Construction of the road began in the summer of 1859 at Fort Walla Walla, the head of navigation on the Columbia River. Lieutenant John Mullan of the U.S. Topographical Engineers commanded a work detail of 140 civilians and soldiers that hacked, blasted, and carved a road eastward toward Fort Benton through northern Idaho and western Montana. The U.S. Army intended the road to carry troops and supplies from the upper reaches of the Missouri River across the Continental Divide to the Pacific Northwest. Mullan needed to complete the road to Fort Benton by August 1, 1860 in order to meet troops there and then escort them back across the newly completed road.
On July 2, 1860, the steamboat Chippewa, and Key West deposited 300 soldiers under the command of Major George Blake at the Fort Benton levee. Among the troops was Lieutenant August Kautz, a Military Academy classmate of Mullan. The soldiers anxiously awaited the arrival of Mullan, who was ordered to lead them back across the newly completed road to Walla Walla. After nearly a month, Mullan and his men arrived at Fort Benton, the road completed on time and a little over budget. Mullan left Fort Benton a few days ahead of Blake's recruits, improving the road in advance of the soldiers. After marching
over two months and covering more than 600 miles, the soldiers reached Walla Walla. It was the only time the Mullan Road was used as a military road.