It Is Just A Matter Of Perspective.

A view straight up the north leg of the Gateway Arch in St. Louis.

The arch was built between 1963 and 1968. It is the only building in the world based on the Catenary Arch. It stands 630 feet (192 m) tall and 630 feet (192 m) wide at its base. The legs triangular and are 54 feet (16.5 m) wide on each side at the base, narrowing to 17 feet (5.2 m) at the arch. The outer cover of the arch is welded stainless steel plates.

Source – Wikipedia

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This image showing people walking by gives a perspective of size of the leg at the base.

Nikon D40X with 18X55mm Nikon lens on Auto.