The city was founded in 1764 by French fur traders Pierre Laclede and Auguste Chouteau and under the French flag. Little did they know that the land had already been ceded to Spain via the secret Treaty of Fontainebleau in 1762. Spanish governors did not reach St. Louis until 1767 and St. Louis was still administered largely by a Frenchman named St. Ange until 1770, when Pedro Piernas took over as the Spanish Governor of St. Louis. He reported to the governor of Louisiana for Spain, Don Alejandro O’Reilly, who was headquartered in New Orleans.
The Third Treaty of San Ildefonso returned the Louisiana Territories (including St. Louis) to France, which was by that time under the rule of Napoleon. However, the French never sent a governor to St. Louis, so it was the Spanish governor, Delassus, who handed the city over to the Americans. One of the interesting things about the Spanish administration in Louisiana is that it reflects what a global force Spain still was. It attracted all nationalities to work in its ranks, including the Irishman O’Reilly and Delassus, who was a refugee from the French revolution.