Located on the western bank of the Mississippi River, the Gateway Arch is the 630-foot centerpiece of the National Memorial. Landscape architect Dan Kiley teamed with Eero Saarinen in a 1947-1948 design competition, culminating in a 91-acre park that commemorates the 1804 departure of the Lewis and Clark expedition and St. Louis’ role in westward expansion.

The original winning landscape design was asymmetrical and heavily wooded, envisioning Saarinen's Gateway Arch rising from an urban forest. Implementation was delayed by conflict over railroad trestles running through the site and a lack of funding. When funding became available in 1957, Saarinen and Kiley revisited the original design and created a concept that respected important axial site lines between the Gateway Arch and the Old Courthouse. The sweeping landscape reflects the curve of the Arch, repeating the curvature in walkways, stairs, and site walls. Kiley’s application of geometrical details and classical design elements subtly root the monument in the landscape.

The Gateway Arch was completed in 1965, and the landscape construction followed for more than a decade. The site was listed on the National Register of Historic Places in 1976 and designated a National Historic Landmark in 1987.