City (pop., 2000: 348,189), east-central Missouri, U.S. Located on the Mississippi River below its confluence with the Missouri River , it was founded by Auguste Chouteau in 1764 as a trading post and was named for King Louis IX of France.
It became the crossroads of westward expansion for exploring parties, fur-trading expeditions, and pioneers traveling the Santa Fe and Oregon trails. Since the 19th-century steamboat era and the arrival of the railroads in the 1850s, it has been a major transportation hub. Its diversified industries include brewing, food processing, and the manufacture of aircraft. The largest city in the state, it is home to many educational institutions, including Washington University and St. Louis University. The emblem of the city is its Gateway Arch, designed by Eero Saarinen .