In 1804-06, Captains Meriwether Lewis and William Clark led about 40 soldiers and boatmen on an epic journey after President Thomas Jefferson commissioned this Corps of Discovery to find a route to the Pacific Ocean through the newly acquired Louisiana territory. Along the way, they mapped the land, recorded its resources, and contacted its native inhabitants. The United States had purchased the Louisiana territory, more than 830,000 square miles, from France in 1803. With Jefferson's permission, Lewis asked his friend and former commanding officer, William Clark, to be co-leader, and although opposite in temperament, they worked harmoniously throughout the two-year journey. Since their exploration, the landscape has changed as rivers have been dammed, forests cut over, prairies plowed under, and roads built to the horizon, though remnants of wilderness still exist.