Fort Benton was the eastern terminus of the Mullan Military Road. Construction 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 140 civilians and soldiers who hacked, blasted, and carved the 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, so he could meet troops there and escort them back across the newly completed road. On July 2, 1860, the steamboat Chippewa and Key West deposited 300 soldiers under Major George Blake at the Fort Benton levee, including Lieutenant August Kautz, a Military Academy classmate of Mullan. The soldiers waited nearly a month for Mullan and his men to arrive with the road finished on time and a little over budget. Mullan then left Fort Benton a few days ahead of Blake's recruits, improving the road in advance of the soldiers, who marched more than 600 miles over two months to reach Walla Walla. It was the only time the Mullan Road was used as a military road.