On a dark December afternoon in 1803, a boat moved slowly along the banks of the Mississippi River. There was a group of men in it, and they were all wearing dark clothes, with their faces covered. They didn’t want to be noticed.

The boat landed at the mouth of the wood river in what is now the state of Illinois, and the men climbed out and began to set up camp under some trees.

Suddenly there was a violent storm. There was a lot of rain and snow and the weather was very cold and windy. The men were completely wet and their hands were frozen.

Instead, they worked even harder. They spent the next five months there, preparing for the trip they were about to start.

Among these men were Meriwether Lewis and William Clark. They were the leaders of the expedition.

The president of the United States had asked them to explore the land that the United States had recently bought from France. He knew that these men were strong enough to do what was needed.

Thomas Jefferson became the third President of the United States in 1801. At that time the country stopped at the Mississippi River. France controlled much of the land to the west of river.

Jefferson had decided that it was important for the United States to own it, and not allow dangerous neighbours to live there.

President Jefferson also wanted to buy New Orleans from the French, because it gave access to the Mississippi River, which went through the city, and flowed through parts of the country that were difficult to reach.

Then, in 1803, Jefferson made the Louisiana Purchase, and New Orleans belonged to the United States.

The Tribune