The Gateway Arch is a 630-foot (192 m) monument in St. Louis, Missouri, United States. Clad in stainless steel and built in the form of a weighted catenary arch,[5] it is the world's tallest arch,[4] the tallest man-made monument in the Western Hemisphere,[6] and Missouri's tallest accessible building. Built as a monument to the westward expansion of the United States,[5] and officially dedicated to "the American people," it is the centerpiece of the Gateway Arch National Park and has become an