A 630-Foot Span That Rises the Same Distance
The Gateway Arch’s matching height and width are more than a visual coincidence: the monument measures 630 feet from the ground to its crown and 630 feet between the outer edges of its base. That square proportion can be hard to read from below, where the legs sweep inward and the top seems much farther away than the bases are apart.
The Curve Carries the Load
The Arch follows a weighted catenary—a curve related to the shape a hanging chain makes, adjusted for the structure’s changing thickness. This form helps direct the immense weight down through the two legs and into the foundations. The legs are broad at ground level and narrow toward the crown, so the structure’s shape and mass change together rather than relying on a uniform arc.
Its construction also reflects that geometry. Crews raised the two legs in separate sections, building upward from opposite sides of the span. Each new section had to meet the curve and remain stable as the unfinished legs grew taller; only at the crown could the two sides become one continuous arch.
Why the Proportion Matters
Seen from a distance, the Arch reads as a slender loop. Standing near its base, visitors can look across a span as wide as the structure is high—a scale relationship the rising curve conceals until the full monument is in view.
