Saint Louis Gateway Arch , Missouri
The Arch is the tallest national monument in the United States at 630 feet.
The Arch is a structure known as a catenary curve, the shape a free-hanging chain takes when held at both ends, and considered the most structurally-sound arch shape. The span of the Arch legs at ground level is 630 feet, the same as its height.(Shape of Arch Section Equilateral Triangle)
The Arch sways a maximum of 18" (9" each way) in a 150 mph wind. The usual sway is 1/2".
Capacity of Observation Platform at the top is 100 - 140 persons.