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It is hard to imagine how anyone can build ANY arch, let alone a smoothly-curving 630-foot tall arch that is hollow inside so people can ride a tram to the top!
This is the tallest monument in the United States. Made of stainless steel skin covering a sandwich of two carbon steel walls with reinforced concrete in the middle, on the bottom half, and carbon steel and rebar, on the top half, this monument is exactly as wide as it is tall. The tram is an egg-shaped “elevator” with five seats per compartment and a flat floor. Because there are two bases (one on the north end, and one on the south end), and each base has a train of eight linked compartments, the tram can transport 80 passengers at a time. In each leg of the arch is a stairway for emergency use. I wouldn’t like to be in the top when an emergency occurs—and have to walk down 1,076 steps!
This modern arch is truly and architectural wonder, but people have been making blocky arches since ancient times.