Description: Completed in 1965 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, making it the tallest national monument.
In order to ensure that the constructed legs would meet, the margin of error for failure was 1/64th of an inch. All survey work was done at night to eliminate distortion caused by the sun's rays.
