1803 – Lewis and Clark start their expedition to the west by leaving Pittsburgh at 11 in the morning
. The Lewis and Clark Expedition, also known as the Corps of Discovery Expedition, was the first American expedition to cross what is now the western portion of the United States. It began near St. Louis, made its way westward, and passed through the continental divide to reach the Pacific coast. President Thomas Jefferson commissioned the expedition shortly after the Louisiana Purchase in 1803. It comprised a selected group of U.S. Army volunteers under the command of Captain Meriwether Lewis and his close friend, Second Lieutenant William Clark. Their perilous journey lasted from May 1804 to September 1806. The primary objective was to explore and to map the newly acquired territory, to find a practical route across the western half of the continent, and to establish an American presence in this territory before Britain and other European powers tried to claim it. The campaign's secondary objectives were scientific and economic: to study the area's plants, animal life, and geography, and to establish trade with local Native American tribes. With maps, sketches, and journals in hand, the expedition returned to St. Louis to report its findings to Jefferson.