The Gateway Arch is a 630-foot (192 m) monument in St. Louis in the U.S. state of Missouri. Clad in stainless steel and built in the form of an inverted, weighted catenary arch, it is the world's tallest arch, the tallest man-made monument in the Western Hemisphere, and Missouri's tallest accessible building. Built as a monument to the westward expansion of the United States, it is the centerpiece of the Jefferson National Expansion Memorial and has become an internationally famous symbol of St. Louis.
The arch sits at the site of St. Louis' founding on the west bank of the Mississippi River.
The Gateway Arch was designed by Finnish-American architect Eero Saarinen in 1947; construction began on February 12, 1963, and was completed on October 28, 1965, for $13 million (equivalent to $190 million in 2015). The monument opened to the public on June 10, 1967.