28th October: The Gateway Arch, St Louis

The Gateway Arch was completed in St Louis, Missouri on this date in 1965. Here are ten things you might not know about it:

1. At 630 feet (192m) high it is the world's tallest arch, the tallest man-made monument in the Western Hemisphere, the tallest memorial in the United States, the tallest stainless steel monument in the world and Missouri's tallest accessible building.
2. Its length is also 630 feet (192m), and its shape is a catenary, which in physics is the curve that a hanging chain or cable assumes under its own weight when supported only at its ends.
3. It was built as a monument to the westward expansion of the United States. The south leg of the arch is near to the spot where a trader named Pierre Laclede marked a tree with an axe in 1763 in order to mark the site of his fur trading post, which grew into a French colonial town which eventually became the city of St Louis.
4. The architect was Finnish-American Eero Saarinen.
5. The arch is made from 886 tons of stainless steel and 38,107 tons of concrete. It was was designed to withstand an Earthquake. The top of the arch won’t sway until the wind blows about 50 miles per hour, and then it would only move 1 ½ inches.
6. Like most new monuments, there was a mixed reaction to it. It was described variously as "a modern monument, fitting, beautiful and impressive."or a "stupendous hairpin and a stainless steel hitching post."
7. There are three ways up (and down). There is an elevator, emergency stairs in each leg with 1,076 steps, and a tram, which is the way the million or so visitors per year get up. The tram is described as a combination of a Ferris wheel and an elevator. It takes four minutes to get to the top.
8. The observation deck is 65 feet (20 m) long and 7 feet (2.1 m) wide and can hold up to 160 people. It has 16 windows on each side, each measuring 7 by 27 inches (180 mm × 690 mm), which offer views of up to 30 miles (48 km).
9. At the topping out ceremony, a time capsule, containing the signatures of 762,000 students and others, was welded into the keystone. A Catholic priest and a rabbi prayed over the keystone, and then Vice President Hubert Humphrey observed from a Helicopter as the keystone was put in place. This wasn't straightforward. The metal in the arch had expanded with the heat and had to be sprayed with fire hoses to cool it down before the keystone would fit.
10. The arch is featured in the sci-fi series Defiance. In the programme the apex is used as a radio station studio, with the arch itself acting as the station's antenna.