St. Louis was founded by French settlers in 1764 and developed as a center of French culture and Spanish power. With the United States’ Louisiana Purchase in 1803, it soon became a major point of departure for western-bound emigrants. The Jefferson National Expansion Memorial is on the site of the original downtown. The memorial comprises the Gateway Arch (a National Historic Landmark), the Museum of Westward Expansion, and St. Louis’ Old Courthouse. Architect Eero Saarinen’s design for a 630-foot stainless steel catenary arch was selected in 1947, and construction began in the 1960s. The Gateway Arch is the tallest monument in the United States. Below the Arch lies the Museum of Westward Expansion, which houses an extensive collection of artifacts and an overview of the Lewis and Clark Expedition. The nearby Old Courthouse, built in 1839, is one of the oldest extant buildings in St. Louis.