ST. LOUIS – Once the fourth-largest U.S. city, St. Louis has a rich history that gets celebrated around this time every year. Muddled through years of tradition, the city’s actual birthdate.

As history tells, the city of St. Louis was founded in February 1764. French fur traders Pierre Laclède and Auguste Chouteau settled after a trek from Illinois, and the city earned it namesake after Louis IX of France.

When did all of this happen? Some historians will tell you Valentine’s Day. Others will tell you the day after. St. Louis’ actual birthday has been debated for centuries. Not even some of the oldest pieces of documentation saved can quite pinpoint the exact date of its discovery.

The Missouri History Museum opted to recognize St. Louis’ founding date (informal birthday) on Tuesday. Organizers shared one of the oldest-preserved pieces of evidence of St. Louis as a settlement: a $10 banknote by the Bank of St. Louis, which shows the Chouteau Mansion, but no key dates.

Fred Fausz, associate professor of history at UMSL, and the Historical Marker Database contend the founding date was Feb. 15. The database claims Chouteau led his workers to began building up on the later date.

It’s a mystery the world may never know, but the narrative behind the founding of St. Louis is widely accepted. St. Louis was a settlement of Native American mound-builders from as early as the 9th century to the 15th century. Spain claimed the area as a trading post in 1763, but reached an agreement with France that paved the way for civilization in St. Louis the following year.

The city of St. Louis officially became part of the United States through the Louisiana Purchase in 1803 and part of Missouri when it claimed statehood in 1821.