Stairs seem so simple, so obvious.
But most early construction was out, not up. It wasn't until cultures became more sophisticated that steps were incorporated into structures.
Eventually, stairs became a science. The height, the depth — we have the staircase all figured out, thanks in part to Peter Nicholson, a Scotsman who wrote "A treatise on the construction of staircases and handrails ... Preceded by some necessary problems in practical geometry" in 1820.
Nicholson laid out the necessary components of a staircase: the "rough strings," placed under the steps perpendicular to the wall; the newel, or posts at the top of the flight; the bracketed stair, with notched rough strings; the pitching piece, to which the rough strings are attached at the top.
The curtain, the swan-neck, the knee — Nicholson revealed the details behind the ascent. But his book also contained a new invention: the curved staircase.
It was not just an innovation; it was an aesthetic leap. So much so that by the late 1820s, all of the smartest homes had graceful curved staircases with equally graceful curved handrails. Unlike gimmicky designs that go out of vogue just as quickly as they come into it, the curved staircase endured because it brought beauty and grace to something so plain and pedestrian.
Consider the staircase in the Rand Tower in Minneapolis.
Rufus Rand, a World War I aviator and utility magnate, commissioned the Rand, which would become Minneapolis' most modern skyscraper. He chose the finest talents of the time: Holabird & Root, a Chicago firm noted for its crisp modern designs. But the staircase, which pours down into the 1929 building's silvered lobby, revealed a romantic rather than modern sense of design.