In 1803, Jefferson named his private secretary and fellow Virginian, 29-year-old Meriwether Lewis, as the commander of the Western expedition [source: University of Virginia]. Lewis (1774-1809), an accomplished sharpshooter and experienced outdoorsman, had served as an Army captain in the Northwest Territory. He chose William Clark (1770-1838), a friend from the Army, as his co-captain. Lewis felt that Clark possessed the right balance of physical strength and intellect to help lead a crew on an uncharted voyage of discovery -- and he also had a reputation as a mapmaker, so he became the official cartographer of the party. His final map of the Lewis and Clark Trail is accurate within 40 miles, though it spans a distance of 8,000 miles.
In his final instructions to the explorers, Jefferson stated that "…the object of your mission is to explore the Missouri River, and such principal streams of it, by its course and communication with the waters of the Columbia, Oregon, Colorado or any other river, may offer the most direct and practicable water communication across this continent for the purposes of commerce" [source: National Park Service].
A direct water route from sea to sea may have been Jefferson's main aim, but it wasn't his only goal for the expedition. Jefferson, like all Enlightenment thinkers, wanted to use science to shape the expedition. He told the explorers to collect, classify, document and observe the landscape, its wildlife and people with scientific precision. That's why there is such an abundance of information about the journey -- most of the members kept journals, took detailed notes and mapped the terrain as they went forward.
Because the expedition crew would most likely be running into American Indian tribes on their journey, Jefferson also wanted them to be fluent in the nuances of sign language, the rituals of diplomacy and the subtle symbols of military power. The men had to study up on the social mores of different tribes -- they had to know tribal hierarchy, how to behave properly in ritual ceremonies, which tribes were dangerous and which colors were sacred or offensive.
After months of preparation, it was time to set off. Lewis gathered a partial crew in Pittsburgh, Pa.