The bloodiest single incident in the Kansas-Missouri border struggles from 1854 to 1861 occurred on May 19, 1858, when about 30 proslavery Missourians seized 11 Kansas Free-State men near Trading Post and marched them to a ravine 225 yards northwest, where they lined up their prisoners and shot them down, killing five and wounding five others; one escaped injury by feigning death. Northerners were horrified, and John Greenleaf Whittier immortalized the fallen in the poem "Le Marais du Cygne." A few weeks after the massacre, John Brown arrived and built a two-story log fort about 14 by 18 feet, which he occupied with a few men through the summer. In December he made a raid into Missouri in which 11 slaves were liberated and one man was killed. Brown's famous "Parallels," dated January 3, 1859, at Trading Post, argued that "hell is stirred from beneath" because of his raid while no comparable action had been taken to find and punish the Marais des Cygnes murderers. A Brown follower, Charles C. Hadsall, bought the property in 1858 and later built the stone house standing adjacent to the fort site. The building and grounds were presented to the State of Kansas in 1941 by Pleasanton Post, Veterans of Foreign Wars.