The 17th-century French architect, engineer, diplomat, and author Francois Blondel is best remembered for a fairly obscure achievement: He developed a formula that established the ideal ratio between a stair’s riser and tread. Writing in his 1683 Cours d’Architecture, he decreed that for every unit of increase in height, the depth should increase by two units, and that two risers plus one tread—the distance covered in one human step—should be roughly 25 inches.

That formula remains etched in many building codes today—one of the few constants in a remarkably diverse form. Staircases can be free-standing or ballustraded. They can be helical, elliptical, or spiral. They can turn at landings in an L- or a U-shape. They can use perpendicular steps or twist with angled wedges. They can cantilever out from the wall. They can also be dangerous: As Bill Bryson writes in his 2010 At Home, a profile of the English rectory he lives in, falling down staircases is the second-most common cause of accidental deaths, after car crashes. 

The advent of elevators and escalators has marginalized the use of interior stairs in public buildings, and truly monumental exterior staircases are also on the wane. In The New York Times in 1987, architecture critic Paul Goldberger wrote, “It is not a question of technology, or even of fashion. It is more one of democracy: A huge outdoor staircase is not accessible to everyone, and today, equal access for the handicapped and the elderly has become a determining factor in architecture.” 

This slideshow presents some of the most stunning examples of this declining art form, from the corkscrewing entryway to a famed Le Corbusier housing unit to the swooping steps of a Bernard Tschumi, FAIA, concert hall, all captured by Esto photographers.