There’s hardly a more recognizable landmark in the Midwest than St. Louis’s towering Gateway Arch, a 630-foot-tall monument to Thomas Jefferson and his ideas for America’s westward expansion. It’s the tallest monument in the United States and the tallest arch in the world. Designed by the American-Finnish architect Eero Saarinen, the arch was an engineering feat—in fact, many people didn’t think it would stand. But as a testament to the architects, engineers, and workers who built it, the Gateway Arch has long stood the test of time. It officially opened in 1965 (sadly, four years after Saarinen’s death), and it’s drawn millions of visitors since. Though it’s an iconic landmark, there are a number of facts you might not know about the Gateway Arch. Here, we present eight of them.

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1. Forty blocks of St. Louis were demolished to build the arch and its surrounding park.

In what St. Louis city engineer W. C. Bernard called “an enforced slum-clearance program,” dozens of warehouses and cast-iron buildings housing 290 businesses were razed to create space for the arch. It was a controversial move—particularly since it was discovered that the vote to allocate city funds to the project was rigged.

2. The arch’s two legs were built separately, and if their measurements were off by as little as 1/64th of an inch, they would not have been able to join at the top.

The stainless-steel pieces of the arch were shipped in via train from Pennsylvania and had to be assembled on site. Welders had to work extraordinarily carefully to ensure their measurements were precise—the margin of error allowed was less than half a millimeter. Though the construction workers were sure of their product, many people speculated that the arch would fail when the last piece at the top of the arch was set in place to join the legs. It didn’t, of course.

3. The insurance company for the project predicted that 13 workers would die during construction.

With a difficult construction process that saw people working hundreds of feet in the air with no safety nets, it’s not too much of a surprise that the insurers expected there to be fatalities. But somehow, no one died during construction. The only death associated with the Gateway Arch was that of Kenneth Swyers, who in 1980 leaped from a plane, parachuted to the top of the arch, and attempted to BASE-jump to the ground. His auxiliary parachute didn’t deploy, and he fell to his death.

4. There was confusion over whether Eliel or Eero Saarinen won the design competition for the monument.

Both father and son entered the competition, and even though Eero was chosen as the winner, confused officials mistakenly told Eliel he had won. The architects and their family had already had a Champagne celebration to toast the senior Saarinen when a telegram came in to correct the error.

5. The arch is as tall as it is wide.

Though it might not look like it, the arch is 630 feet tall and 630 feet wide. Since you’re not always looking at the arch straight on, you experience an illusion that it’s much taller than it is wide.

6. The unique tram system was invented by a man with no formal engineering training.

Thanks to the curved shape of the arch, a regular elevator couldn’t bring visitors from the base to the top. Saarinen’s firm called the Montgomery Elevator Company in Moline, Illinois, to solve the problem. Dick Bowser, a college dropout whose family was in the elevator business, happened to visit a friend who worked at the company, and that friend connected him with the architect. Bowser was asked to design the system in just two weeks. His solution was a tram that was part elevator and part ferris wheel—it’s the very system that lifts visitors to the top of the arch today.

7. Presidents aren’t allowed to go to the top—except President Eisenhower.

The Secret Service has forbidden all presidents from ascending the Gateway Arch due to security concerns—it is, after all, a very tight, enclosed space. The only exception was Dwight D. Eisenhower, who signed the order for the construction of the arch in 1954. In 1967, when he was 77 years old, the former president visited St. Louis to give a speech. A trip to the top was not in his itinerary, but when he showed up early to the monument (after it had closed to the public), he insisted on riding the tram up.

8. The arch’s current renovation is more than twice as expensive as the original cost to build it.

When the arch was built in the early 1960s, it cost $13 million to build, or more $100 million today when adjusted for inflation. The arch is currently undergoing a $380 million refurbishment that saw the renovation of the park, the expansion of the museum, the addition of a cafe, and the raising of the riverbank to prevent flooding. The five-year project will be complete in July.