11/20/2009:
The Lewis and Clark expedition began their ascent up the Mississippi River on this day in 1803. The group, under the direction of Meriwether Lewis and William Clark, was composed of a ragtag band of military men, interpreters, traders, and boatmen. Although Lewis had originally intended to recruit fifteen men for the expedition, it was necessary to hire several more boatmen in Illinois Country - as the area was then known - in order to move the group's two large keelboats up the Mississippi on their way to the Missouri river.
In 1803, the group was forced to winter on the east side of the Mississippi shortly after setting off from Illinois. This was because Spanish forces were still in control of the Louisiana Territory, and word of the United States' purchase of the territory from France had not yet reached Spanish forces on the western side of the river.
Shortly after leaving Fort Kaskaskia in Illinois, the group reached the site of Cahokia on December 6th. Cahokia, near present-day St. Louis, is now known as the country's largest archaeological site. The abandoned Native American city contained a large complex of earthen mounds. It was also home to a small number of French and American traders. Lewis engaged two of the residents, John Hay and Nicholas Jarrot, to ferry him across the Mississippi to meet with Spanish forces in St. Louis. The Spanish Commandant was not able to grant the expedition permission to cross the Mississippi, as he had not yet received word of the purchase. Although France legally owned the Louisiana Territory, the land had only been transferred from Spanish hands in a secret agreement between Napoleon and Spain's King Charles IV in 1800. The territory had originally been owned by France, of course, but was granted to Spain for their help in the French and Indian War in 1763. So, when King Charles secretly returned the territory to France in 1800, Spanish forces were kept in the territory to maintain the impression that the area was still a Spanish possession.
Word did eventually reach the west side of the Mississippi, however, and the expedition was allowed to move into the territory President Thomas Jefferson had sent them to investigate. The long trip up the Missouri river began, with the expedition still a long way from what would become the winter camp at the Mandan villages near present-day Bismarck.
Sources:
http://www.campdubois.com/html/history.html
http://www.shgresources.com/nd/timeline/
http://lewis-clark.org/content/content-article.asp?ArticleID=332#