What Was the Lewis and Clark Expedition?

When Meriwether Lewis, William Clark, and the "Corps of Discovery" left St. Louis, Missouri, on May 21, 1804, their mission was to explore the vast, unknown territory acquired a year earlier in the Louisiana Purchase. The travellers hoped to find a waterway that crossed the western half of the United States. They didn't. But their two-year journey finally brought them to the Pacific Ocean.