The Gateway Arch was built in 1963 and finished in 1965.  It is the tallest National Monument in the United States.  It is made of steel and is built on a curve or arch called the catenary curve.  It has trams that carry about a million people to the top to see a great view of St. Louis, Missouri, and the countryside beyond the city limits.  It is right at the riverfront, and many people who visit, want to experience the ride and the view.  There is a Museum dedicated to Indians and the old west, located underneath the arch, and also you can view a small movie about the two year construction process  of the arch.  In order for the arch to be stable and fit in its existing site, it is said that it had to be precisely 630 feet tall, and 630 feet wide and the  margin of error factor could be no more than and 1/8th of an inch.  Since it has been standing and functioning for years, you can see that they built it correctly.