On this day in 1866, construction began on the most important army outpost in the west. Fort Phil Kearney guarded the Bozeman Trail, a branch of the Oregon Trail that headed northwest to Montana. The trail passed through Sioux hunting grounds and wagon trains were under constant attacks from Chief Red Cloud. Though its legality was questionable, the fort was built in a choice location in northern Wyoming. By the time construction was finished, the fort consisted of thirty buildings. Indian attacks were numerous and it became nearly impossible to stop them. By 1868, the United States government abandoned all forts and closed the trail in exchange for peace with the Indians. Once the soldiers left, the Indians burned Fort Phil Kearney to the ground.