St. Louis is considered the Gateway to the West, and there’s a reason for that. On May 14, 1804, William Clark and his Corps of Discovery departed from a fort near St. Louis at the Mississippi River to begin a two-year exploration of the land acquired in the Louisiana Purchase. On this day (May 21) in 1804, Meriwether Lewis joined Clark in the then-settlement of St. Charles, Mo., and together they led the Corps on the first American expedition west of the Mississippi. As we all know, it reached the Pacific Ocean; it also paved the way for Americans to live and thrive in the newly acquired western territory.

Here are 14 things you should know about the trip:

1. The expedition was ordered in by President Thomas Jefferson, who guided the Louisiana Purchase the year before.

2. Meriwether Lewis was Jefferson’s personal secretary.

3. William Clark, recruited by Lewis, was never officially recognized by the government as a co-captain of the expedition.

4. Jefferson’s goal was for Lewis and Clark to find a water route linking the Columbia and Missouri rivers to increase western access to port markets and eastern cities.

5. Items the duo packed included 45 flannel shirts, 106 liters of salt, vermilion face paint (as a present for Indian tribes), and 176 pounds of gunpowder…

6. …and their black Newfoundland dog named Seaman. He became the only animal to complete the journey west to the Pacific!

7. Lewis and Clark established diplomatic relationships with several Native American tribes along the way – some of whom were a great help to the expedition. (The Shoshone Indians actually helped them cross the Bitterroot Mountains on horseback.)

8. Sacagawea, a Shoshone, served as an interpreter between Lewis and Clark and her tribe.

9. The Coyote, the Grizzly Bear and the Prickly-Pear Cactus were among the 300 plant/animal species Lewis and Clark discovered.

10. Oh yeah, and the duo also discovered the Rocky Mountains.

11. The duo produced detailed maps of the land and water they encountered on their journey – including creeks and spots where they camped – paving the way for future explorers.

12. Their expedition sparked a flow of immigration to and development of the western U.S. territory.

13. The increase in western development displaced many of the Indians who originally had good relationships with Americans due to Lewis and Clark. The flood of immigration forced them onto reservations.

14. Thomas Jefferson had originally expected Lewis and Clark to find woolly mammoths, erupting volcanoes and a mountain of pure salt on their journey.

Thanks, Lewis and Clark, for all your discoveries and for helping to make St. Louis the true Gateway to the West!

Sources: Archives.gov, NationalGeographic.com