The Gateway Arch in St. Louis, Missouri, the iconic symbol of the city. The monument honors the westward expansion of the United States, much of which began in this city. Built between 1963 and 1965 (but not opened to the public until 1967), the stainless steel-sheathed structure is hollow to accommodate a unique tram system that takes visitors to an observation deck at the top. Both the height and width of the arch are 192 m (630 ft). The structure is the tallest monument in the United States and the tallest stainless steel monument in the world.