How the design was chosen: There was a nationwide competition in 1947-1948 to design a monument in St. Louis honoring western pioneers. The architect Eero Saarinen (August 20, 1910 - September 1, 1961) won the contest with his sleek arch.
Construction: Construction of the arch began on February 12, 1963, and was finished on October 28, 1965. It was opened to the public on July 24, 1967. (after one of the trams was completed). It cost about 13 million dollars to build. The two bases are equilateral triangles (triangles with three 54 foot-long sides). At the top of the arch, the triangle is only 17 feet long on each side. Visitors enter the arch from an underground visitors center and can travel to the observation deck at the top in a 40-passenger tram that runs inside the arch.
The arch has 60-foot deep foundations. The arch is very stable and was built to withstand high winds and earthquakes. The structure sways about one inch in a 20 mph wind; it is designed to sway up to 18 inches in 150 mile per hour winds.
The Arch: The St. Louis Gateway Arch is in the form of an inverted catenary, which is a very stable structure that is often used in bridges, domes, and arches.
A catenary is the shape that a chain or necklace forms when held by the two ends. The Dutch mathematician Christiaan Huygens named this curve from the Latin word catenarius, which means "related to a chain."
The equation for a catenary curve is: y = k cosh(x/k) , where cosh is the hyperbolic cosine [cosh(x) = (ex + e-x)/2] and k is the y-intercept (where the curve hits the y-axis).