The St. Louis Arch Defies All Expectations

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Welders working on the Gateway Arch were tasked with an almost impossibly narrow margin for error—less than half a millimeter (0.01 inches). This small tolerance was crucial when they inserted the final piece of the towering structure. Despite its sleek, 630-foot (192-meter) appearance, the Arch's legs were constructed separately, with stainless steel shipped by train from Pennsylvania. When work began in 1961, many believed the project would end in failure, questioning how workers could ensure the exact space needed for the last piece with no room for mistakes.

Against all odds, the team succeeded, cementing the Gateway Arch’s status as the tallest monument in America and the tallest arch in the world. The feat was made possible by the innovative design of American-Finnish architect Eero Saarinen, who won a contest with his ambitious vision. But the story behind the Arch’s creation is even more intriguing.

"Gateway Arch National Park is an exceptional site managed by the National Park Service," shares NPS historian Bob Moore. "Its origins are equally remarkable. In the early 1930s, a middle-aged lawyer with thick glasses and a self-described mission to do good, named Luther Ely Smith, proposed the idea of transforming the deteriorating St. Louis riverfront. In those pre-commercial aviation days, the riverfront was the first sight people saw as they approached the city by train or car."

As Moore points out, the riverfront in the 1930s did little to impress visitors. "It wasn’t an attractive sight and didn’t give people the impression that St. Louis was one of America’s great cities," Moore explains. "The buildings along the river were old and worn out." With modern barges replacing the classic paddle-wheel steamboats, the once-thriving harbor had fallen into neglect, as the action shifted to other locations. "Smith's aim was twofold: to rejuvenate the city and provide employment during the Great Depression," Moore notes. "Additionally, he envisioned creating a unique memorial to attract visitors from around the world."

While ideas for revitalizing the riverfront had been proposed since 1898, Smith was the one with the resolve and influence to bring his vision to life, as Moore observes. At the core of Smith’s plan was a tribute to commemorate a significant event in U.S. history—the migration of hundreds of thousands of people westward through St. Louis in the 19th century, which marked the city as the last major urban hub before the frontier.

The Competition for an Architect

In 1947, just two years after the conclusion of World War II, a committee of St. Louis citizens launched an architectural competition aimed at transforming the city’s riverfront. The competition was open to any U.S. architect, offering a $225,000 cash prize for the winner. As Moore explains, the goal of the Jefferson National Expansion Memorial Association was for the memorial area to become an essential part of the community and to enhance the beauty of the surrounding downtown area.

The competition was held in two stages and featured a prestigious jury of renowned architects such as George Howe and William Wurster, who favored a modern architectural style. Influential figures like Walter Gropius, Charles Eames, and Kazumi Adachi entered the competition, which attracted a total of 172 submissions. However, the judges ultimately chose one exceptional contender, although not without some twists.

"When the five semi-finalists were announced in the fall of 1947, competition adviser George Howe telegraphed Eliel Saarinen to inform him that he had been selected as one of the finalists, and that he should prepare a revised design for the next round of judging in early 1948," Moore recounts. At the Saarinen studio in Michigan, the announcement was met with celebration. However, a few days later, Howe had to make an awkward call to explain that Eliel was not among the finalists — it was his son, Eero, who had earned the semi-finalist spot with his bold design for a towering, stainless steel arch. Eliel, ever the supportive father, toasted to Eero’s success with a second bottle of champagne.

Eero Saarinen Is Chosen

Eero officially secured the top prize on February 18, 1948. In a March 7, 1948 article for the St. Louis Post-Dispatch titled "The Arch Began With Pipe Cleaners" (courtesy of the Gateway Arch National Park Archives), Saarinen explained that the concept for the arch was born from his desire to replicate the striking geometric shapes of the iconic monuments to Washington, Lincoln, and Jefferson.

"We started imagining a dome, one much more open than the Jefferson Memorial in Washington," Saarinen wrote. "Perhaps it could be a massive concrete dome with only three points touching the ground. . . . We initially created a rough version using pipe cleaners, but the three-legged structure didn’t work, so we reimagined it with just two legs, forming a large arch. . . . Over time, we realized the arch was a gateway, and friends who took a closer look immediately recognized it as such. Eventually, we named it the 'Gateway to the West.'"

Designing a massive, sweeping structure is no simple task. "In the Arch's design, extensive studies were conducted to find the correct curvature," explained architect Kevin Roche, who collaborated with Saarinen on the final design and completed the project after Saarinen's death in 1961. In a document from the Gateway Arch National Park Archives titled "Designing the Arch," Roche noted, "While the curve resembled a catenary, such as one formed by a hanging chain, the design process also involved studying how a weighted catenary would slightly alter the simple catenary form. This process included many models, studies, section drawings, and experiments with chains suspended from the ceiling with weights."

The actual structural design of the Gateway Arch was the work of engineer Fred Severud, with assistance from his associate Hannskarl Bandel. In a document from the Gateway Arch National Park Archives, Severud's son, Fred Jr., recounted, "Although Eero Saarinen designed the appearance of the Arch, it was my father and his firm that determined how it could be constructed. Without the mathematical calculations by the Severud firm, and the use of orthotropic engineering principles (meaning the Arch’s steel inner and outer walls serve as the structural elements, rather than relying on a framework of girders with steel panels suspended from them), the Arch would not exist today. After years of consultation and hard work, construction finally began in 1963."

Severud's son provided a detailed account of his father's intricate plan. "The Arch was constructed as two cantilevered structures that eventually converged at the top," he explained. "The design had to factor in loads and structural behavior at different stages, while also considering the practicalities of construction. During the initial cantilever phase, post-tensioned concrete was placed between the inner and outer walls up to a height of 300 feet (91 meters) to give the necessary strength to support the inward curve of the legs. Above 300 feet (91 meters), the post-tensioned concrete was no longer used."

Due to the Arch's immense height, conventional cranes were not sufficient for the task. As a result, the construction team had to employ a climbing crane, alongside the contractors, on each leg of the Arch. "At around 500 feet (152 meters), a temporary horizontal strut truss was placed across the legs, causing them to work together as a single unit, creating an entirely different stress condition," he wrote.

The Shape of the Curve

Determining the precise shape of the Arch wasn’t straightforward. "The process of finding the curve for the Arch involved suspending a rope from two fixed points; the sag of the rope formed a catenary curve, essentially an upside-down arch," architect Bruce Detmers explained in a document from The Gateway Arch National Park Archives. "Adding weights along the length of the rope altered the curve's shape. A uniformly weighted rope created a curve that was too flat on top. Despite these attempts, the weighted rope did not produce the shape that satisfied Eero's vision."

Bandel, Severud's assistant, played a crucial role in the project, as Detmers explained. 'Adjustments were made to the formula, which were then plotted,' Detmers wrote. 'The process of plotting and creating study models eventually led to the final Arch design. The Arch's legs are more vertical and broader at the base, while the top is smaller and less flat compared to a purely uniformly weighted arch, giving it the appearance of soaring.' The final stage in defining the Arch involved intricate mathematical calculations that took hours to complete. 'Our accounting department's mechanical machine could multiply tracking numbers to several decimal places,' Detmers wrote. 'This outdated technology was used to determine the Arch's dimensions. I was relieved to learn that Pittsburgh Des Moines Steel, the subcontractor fabricating the Arch structure, used a computer to verify our calculations and found no errors.'

The primary challenge, amidst many others, was ensuring the right amount of space for the final connecting piece at the top. Any deviation, whether too much or too little space, would ruin the entire structure. An additional complication arose from the weather. 'Since the final piece had to be set during warm weather, an issue came up,' Severud's son explained. 'The legs were exposed to the sun differently, causing them to vary in height by several feet throughout the day. So, measurements were taken at night when the temperature difference didn’t exist. The construction team also decided to place the final piece at night to ensure proper alignment on both sides.'

The mayor of St. Louis, however, thought this plan was ludicrous. 'This was supposed to be one of the most momentous events in St. Louis history, and it must happen in the early afternoon!' Severud’s son wrote, recounting the mayor’s disbelief. 'This would lead to an elevation difference that couldn't be fixed—what were we to do? My father had an idea one night: use water to cool the heated side! The fire chief was contacted, and he agreed to provide hoses and pumps to spray the hot side. As a result, the final piece was successfully placed during the day without issue.'

Getting People to the Top

The last obstacle to tackle was how to transport visitors to the top of the towering monument. A traditional elevator simply couldn’t work with such a curved structure. This issue was solved by Dick Bowser, a college dropout working at the Montgomery Elevator Company in Moline, Illinois. His innovative solution was a tram that merged the functionality of an elevator with that of a Ferris wheel.

'We had numerous discussions with Dick, who proposed the concept of a capsule that could rotate as it ascended from the underground station up the Arch’s leg to the observation platform at the top,' Roche wrote. 'We crafted several models of the underground station and even built a full-sized replica of the five-person capsule to test with passengers of different sizes. Additionally, we constructed a full-size cross-section through the top of the Arch, ensuring the viewing windows would be small enough to remain hidden from the outside, but large enough to give visitors a stunning view. A lot of attention was devoted to this model to make sure that both children and adults of various heights could comfortably reach the viewing windows.'

Even today, 6,700 visitors daily use Bowser's groundbreaking design to take in the view from the Arch's summit. The 630-foot (192-meter) tall structure weighs 43,226 tons (39,214 metric tons), including 900 tons (816 metric tons) of stainless steel, cost $13.4 million to build, and employed hundreds of workers (none of whom perished in the process, despite predictions of 13 deaths). The Arch remains a top national landmark, drawing million visitors annually.