While Native Americans had long established settlements in the area along the river, the first white explorer was Frenchman Sieure de la Verendyre, whose expedition arrived in 1738. Not until the early 1800s did Euro-American frontiersmen come to the area with any regularity, the Lewis and Clark Expedition in 1804 and 1806, George Catlin in 1832, and Prince Maximilian and Karl Bodmer in 1834 being the most notable. In 1830 the American Fur Company established the Fort Clark Trading Post 40 miles upstream on the Missouri River to support trappers. To provide protection for the approaching rail line from the east and the homesteaders who would surely follow, the US Army established two outposts in the area in 1872 and 1873. Fort Greeley (later renamed Fort Hancock) was founded first on the river's east side. On the west side, an infantry post, Fort McKeen, was constructed on bluffs above the confluence of Heart and Missouri Rivers. In 1873 Congress authorized the addition of a cavalry post and changed its designation to Fort Abraham Lincoln when foot soldiers were deemed ineffective against their mounted adversaries. A permanent civilian settlement known as Lincoln was adjacent to the fort's north side.