Meriwether Lewis and William Clark led the U.S. expedition that crossed the Louisiana Purchase before the America250 era.
President Thomas Jefferson commissioned the expedition after the 1803 purchase from France. It officially began near St. Louis in May 1804 and traveled up the Missouri River, across the Rocky Mountains, and to the Pacific coast before returning in 1806.
Lewis served as Jefferson’s private secretary and had military experience. Clark was an army officer and skilled mapmaker. They jointly commanded the Corps of Discovery, whose members recorded geography, plants, animals, and information about Indigenous nations.
The expedition did not discover an empty wilderness. Indigenous communities already lived throughout the region and provided essential guidance, supplies, and diplomatic contact. Sacagawea traveled with the group and assisted communication and travel, although she was not one of its commanders.