Lewis and Clark Expedition

Historical convention of long standing has it that the expedition of Meriwether Lewis and William Clark was dispatched by President Thomas Jefferson in 1804 to explore the newly acquired territory of Louisiana. In fact, the exploration of Louisiana was a secondary part of the mission of Lewis and Clark. Their primary objective, made clear by Jefferson in a number of letters and other documents, was to locate a commercially practical water route across the North American continent. In other words, Lewis and Clark were sent to find the fabled Northwest Passage. That their expedition (1804–1806) coincided with America's acquisition of the vast territory of Louisiana—the entire western portion of the Mississippi's drainage basin—was simply fortuitous (see Figure 1).

By the time Jefferson was elected president in 1800, he had already made three aborted attempts to have some kind of water route between the Mississippi and the Pacific explored. His thinking was simple and consistent with geographical theory of the later Enlightenment: All major rivers had a common source area where their headwaters interlocked. Since a short portage linked the headwaters of the primary eastern branch of the Mississippi (the Ohio) and the headwaters of a major river flowing to the Atlantic (e.g., the Potomac), the Jeffersonian concept of symmetrical geography held that a short portage ought also to link the headwaters of the Mississippi's major western tributary (the Missouri) and a stream, such as the Columbia, flowing to the Pacific. Jefferson impressed on Lewis that his mission had a single overriding objective: to locate this hypothetical short portage between the upper Missouri and upper Columbia, thereby ending a centuries-long search for a water route through or around North America. Jefferson well knew that the country that discovered such a water route would possess enormous commercial advantages, including control over the Indian trade of the interior. To Jefferson, controlling commerce was the most important step to controlling territory, so the mission he set for Lewis and Clark was, first, commercial but with an unwritten imperial objective as well.

Figure 1 A map of Lewis and Clark's track across the western portion of North America, from the Mississippi to the Pacific Ocean

Source: Lewis, S. (Copyist), & Harrison, S. (Engraver). (1814). A map of Lewis and Clarks track. In P. Allen, N. Biddle, W. Clark, & L. Meriwether (Eds.), History of the expedition under the command of Captains Lewis and Clark. Washington, DC: Library of Congress, Geography and Maps Division.

Although Lewis, a long-time family friend of Jefferson's, was selected to lead the expedition, he prevailed on the President to add a co-commander, William Clark, Lewis's former commanding officer in the U.S. Army in Ohio and a close friend. Clark agreed, and after acquiring geographical information from Jefferson's library, learning the rudiments of scientific observation, and acquiring supplies in Pittsburgh, Lewis traveled down the Ohio River in the summer of 1803, picking up Clark near the falls of the Ohio; the two recruited army and other personnel and went into winter encampment across the Mississippi from St. Louis, at that time the jumping-off point for western travel.

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