This Day in History: br Lewis and br Clark Depart May 14, 1804 Meriwether Lewis and William br Clark were commissioned by br U.S. President Thomas Jefferson to lead an expedition of about 45 men to br explore the land purchased from br France as part of the Louisiana Purchase. Nearly doubling the area of the br United States, the land was br largely unexplored by Europeans. Beginning in St. Louis, MO, br the expedition would last br almost two-and-a-half years. The expedition was eventually br accompanied by a French Canadian br fur trader and his Native American wife, Sacagawea. After facing numerous dangers, br the group arrived at the Pacific br Ocean by way of the Columbia br River on November 8, 1805.