The Louisiana region, named for French King Louis XIV, covered territory from the Mississippi River to the Rocky Mountains, between Canada and the Gulf of Mexico. By a treaty dated April 30, 1803, the United States bought the land from France for about $15 million. The Louisiana Purchase, and the explorations that followed, opened the way for Western expansion in America.
Three Flags Day
On March 10, 1804, the US flag was raised over St. Louis, marking the completion of the Louisiana Purchase. This day, along with March 9, is known as Three Flags Day.
The first came on November 30, 1803, when Spain transferred New Orleans to France. Then on December 20, New Orleans and the rest of Louisiana were transferred to the US. Finally, on March 9, 1804, the transfer began in St. Louis. The Spanish flag was lowered, and the French flag hoisted. It would fly for 24 hours before being removed and replaced by the American flag. The event is often called Three Flags Day and it officially cleared the way for Lewis and Clark to begin their expedition westward.