On August 31, 1803, Captain Meriwether Lewis departed from Fort Fayette, today’s Pittsburgh, in the keelboat the Corps of Discovery would take up the Missouri River and, six weeks later, arrived at the Falls of the Ohio and Clarksville, Indiana Territory. It was here, at the town founded by General George Rogers Clark, that Meriwether Lewis and William Clark, the General’s youngest brother, met again for the first time in seven years and commenced the most famous partnership in American history, two men so joined in American lore as to almost be inseparable. 

In 1801, Meriwether Lewis was a Captain serving as the paymaster for the First Infantry Regiment of the United States Army. In March, he received a letter from Thomas Jefferson, the newly inaugurated President, asking Lewis to become his private secretary. Lewis, whose family was friends with the Jefferson clan, accepted at once, and thus began a close working relationship, one in which Jefferson became a father figure to Lewis and mentored his young subordinate on policy matters, including his dreams of western exploration and expansion.

By the time they began to assemble the Corps of Discovery in the summer of 1803, Thomas Jefferson and Meriwether Lewis knew more than anyone else about the Louisiana Territory, that immense wilderness the country had recently purchased from France. Although Jefferson had never ventured more than fifty miles west from Monticello, he had dreamed of the trans-Mississippi and studied the region extensively over the previous two decades, even trying unsuccessfully to send exploratory expeditions on several occasions.