The Gateway Arch is known as the Gateway to the West. It was designed by Finnish-American architect Eero Saarinen and structural engineer Hannskarl Bandel in 1947 and built between 1963 and 1968. It is the only building in the world based on the catenary arch, making it the iconic image of the city. It stands 630 feet (192.024 m) tall and 630 feet (192.024 m) wide at its base. The legs are 54 feet (16.46 m) wide at the base, narrowing to 17 feet (5.18 m) at the arch. There is a unique tram system to carry passengers to the observation room at the top of the arch.