The Gateway Arch

Six hundred thirty feet of stainless steel curve upward from the western bank of the Mississippi. The Gateway Arch is the tallest monument in the United States, and the shape it traces has a name: a weighted catenary. It is the form a hanging chain makes under gravity, inverted and locked in steel, a mathematical curve turned into something you can stand inside and ride to the top.

The story behind it begins in nineteen forty-seven, when the city of Saint Louis held a design competition for a memorial to westward expansion. One hundred seventy-two architects entered. The winning entry came from Eero Saarinen, a Finnish-American designer who had submitted it by accident. The telegram announcing the competition's winner was mistakenly addressed to his father, the architect Eliel Saarinen, who had also entered. The family celebrated Eliel's apparent win before a correction arrived showing that Eero, not his father, had actually won.

Saarinen's final plan called for an arch six hundred thirty feet tall and six hundred thirty feet wide at the base. The two legs would be built separately, converging upward with microscopic precision. The sections were equilateral triangles in cross-section, tapering from fifty-four feet across at the base to seventeen feet at the crown. Each piece was made from stainless steel shipped by train from Pennsylvania.

Construction began in nineteen sixty-three. As the two legs rose toward each other from opposite sides of the riverbank, engineers faced a final problem: steel expands in sun. One leg was warping outward in the Missouri summer heat. Workers sprayed it with water from fire hoses, contracting the metal just enough that the final keystone section, barely three feet wide, slid into place on October twenty-eighth, nineteen sixty-five.

Saarinen never saw it. He had died of a brain tumor in nineteen sixty-one at age fifty-one. The tram system that carries visitors to the observation room at the crown, riding in cramped cylindrical pods up the inside of each leg, opened in nineteen sixty-seven. The arch still draws over two million visitors a year.