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The Gateway Arch, also known as the Gateway to the West, is an integral part of the Jefferson National Expansion Memorialmarker and the iconic image of St. Louis, Missourimarker. It was designed by Finnish-American architect Eero Saarinen and structural engineer Hannskarl Bandel in 1947. It stands tall, and is wide at its base, making it the tallest monument in the United States. Construction of the arch started on February 12, 1963 and was completed on October 28, 1965. The monument opened to the public on July 10, 1967.

The cross-sections of its legs are equilateral triangles, narrowing from per side at the base to at the top. Each wall consists of a stainless steel skin covering a sandwich of two carbon steel walls with reinforced concrete in the middle from ground level to , with carbon steel and rebar from to the peak. The interior of the Arch is hollow and contains a unique transport system leading to an observation deck at the top. The interior of the Arch also contains two emergency stairwells of 1076 steps each, in the event of a need to evacuate the Arch or if a problem develops with the tram system.

The base of each leg at ground level had an engineering tolerance of one sixty-fourth of an inch or the two legs would not meet at the top.

During construction, both legs were built up simultaneously. When the time came to connect both legs together at the apex, thermal expansion of the sunward facing south leg prevented it from aligning precisely with the north leg. This alignment problem was solved when the St. Louis Fire Department sprayed the south leg with water from firehoses until it had cooled to the point where it aligned with the north leg.

It is the tallest habitable structure in Missouri, 7 feet higher than the 623 foot spire of One Kansas City Placemarker in Kansas Citymarker, and 37 feet higher than the roof of Metropolitan Squaremarker in St. Louis, Missourimarker.


Upper north tram queue area
The interior of a tram car.
Eero Saarinen died from a brain tumor four years before the Arch was completed; prior to his death he had decided to incorporate a power lift system to obviate the need to climb the 1000-plus stairs. But the shape of the arch would have made a standard elevator impossible. After approaching several elevator companies who failed to come up with a viable method, Saarinen hired parking-lot elevator designer Richard Bowser to do the job. Skeptical city leaders gave Bowser only two weeks to submit a design, but he succeeded. By 1968, a unique tram system that combined an elevator cable lift system with gimbaled cars functionally similar to ferris wheel gondolas had been installed.

The tram is operated by the quasi-governmental Bi-State Development Agency under an agreement with the NPS.

From the visitor center one may move to either base (one on the north end and the other on the south end) of the Arch and enter the tramway much as one would enter an ordinary elevator, through narrow double doors. The north queue area includes displays which interpret the design and construction of the Gateway Arch; the south queue area includes displays about the St. Louis riverfront during the mid-19th century.

Passing through the doors, passengers in groups of five enter an egg-shaped compartment containing five seats and a flat floor. Because of the car shape, the compartments have sloped ceilings low enough to force taller riders to lean forward while seated (for this reason it's recommended that the tallest of the five passengers in the car sit in the center seat facing the door). Eight compartments are linked to form a train, meaning that both trains have a capacity of 40, and that 80 people can be transported at one time. These compartments individually retain an appropriate level by periodically rotating every 5 degrees, which allows them to maintain the correct orientation while the entire train follows curved tracks up one leg of the arch. The trip to the top of the Arch takes four minutes, and the trip down takes three minutes. The car doors have narrow windows, allowing passengers to see the interior stairways and structure of the Arch during the trip.

Observation area

Gateway Arch view from Observation Area
Near the top of the arch, the rider exits the compartment and climbs a slight grade to enter the arched observation area. Thirty-two small windows (16 per side) measuring allow views across the Mississippi River and southern Illinoismarker with its prominent Mississippian culture mounds to the east at Cahokia Moundsmarker, and the City of Saint Louismarker and St. Louis Countymarker to the west beyond the city. On a clear day, one can see up to thirty miles (48 km).

Mathematics of the Arch

Curvature detail with the windows of the observation deck located around the apex of the arch.
The geometric form of the Arch was set by mathematical equations provided to Saarinen by Dr. Hannskarl Bandel. Bruce Detmers and other architects expressed the geometric form in blueprints with this equation:

y = A \left( \cosh \frac {Cx}{L} - 1 \right) \quad\Leftrightarrow\quad x = \frac {L}{C} \cosh^{-1} \left( 1 + \frac {y}{A} \right),

with the constants

A = \frac {f_c} {Q_b/Q_t - 1} = 68.7672

C = \cosh^{-1} \frac {Q_b}{Q_t} = 3.0022

where fc = is the maximum height of centroid, Qb = is the maximum cross sectional area of arch at base, Qt= is the minimum cross sectional area of arch at top, and L = is the half width of centroid at the base.

This hyperbolic cosine function describes the shape of a catenary. A chain that supports only its own weight forms a catenary; in this configuration, the chain is strictly in tension. An inverted catenary arch that supports only its own weight is strictly in compression, with no shear. The shape is therefore ideal.


The Arch has come to symbolize St. Louis as a "Gateway" between the east and western United States.

Visitors pass through security checkpoints at each entrance to the Arch enroute to the visitor center. Security was increased due to a 1997 congressional mandate to establish a Counter-Terrorism Program at the park. The NPS used the increased funding to purchase magnetometers and x-ray equipment for visitor screening and 25 CCTV cameras scattered throughout the grounds of the memorial. There are barriers around the grounds to exclude rogue vehicles.

Notable events

A time capsule containing the signatures of 762,000 St. Louis area students was welded into the keystone before that final piece was set in place.

Eleven light aircraft have been successfully flown beneath the arch, the first on June 22, 1966 when the arch had been completed for less than a year.

In 1980, Kenneth Swyers tried to parachute onto the Gateway Arch, planning to jump off to land on the ground. Instead, he slid all the way down one leg to his death. The pilot, Richard Skurat, had his pilot certificate suspended for 90 days.

In 1984, David Adcock of Houston, Texasmarker, began to scale the arch by means of suction cups on his hands and feet, but he was talked out of continuing after having climbed only . The next day he successfully scaled the nearby 21-story Equitable Building in downtown St. Louis.

It was declared a National Historic Landmark in 1987.

On September 14, 1992, it was rumored that John C. Vincent of New Orleansmarker successfully scaled the outside of the Arch with suction cups during the night, and performed a BASE jump from the top with a parachute at 7 a.m. No evidence surfaced to support his claim, and it was speculated by Park Rangers that Vincent was lowered from a helicopter onto the top of the Arch, from which he parachuted. He was jailed three months for the stunt. Jump from Terrifying Heights

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On July 21, 2007, approximately 200 people were trapped in the trams or at the top of the Arch after an electrical problem occurred with the tram system. All were returned to the ground either by being taken down stairs to a service elevator, or by waiting for power to be restored. A second electrical problem caused one tram to be taken out of service the following day.

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