Meriwether Lewis and William Clark, at the request of President Thomas Jefferson, led an expedition to survey the land West of the Mississippi, known as Louisiana Territory, that had been purchased from France in 1803. Lewis, Clark and the rest of their expedition began their journey near St. Louis, Missouri, in May 1804. This group—often called the Corps of Discovery by historians—faced nearly every obstacle and hardship imaginable on their trip. They braved dangerous waters and harsh weather and endured hunger, illness, injury and fatigue. During their first winter, they recieved help and guidance from Sacagawea, a Shoshone Indian.