When is a flight of stairs more than a way to move from one level to the next?

When it is bedazzled by intelligent feet.

When those feet are made of wings.

For the tap dancer Bill (Bojangles) Robinson — who had that feet-as-wings thing down — gliding up and down the zig and the zag of his portable staircase in the 1932 film “Harlem Is Heaven” was an art form all its own.

Stairs won’t talk back or accidentally step on your foot. Instead, they create life. With Robinson, it’s like watching a conversation unfold between a jagged surface and a master of muscular control.

Here, rhythmic accents of agile feet, gently tilted toward the toes, course through an erect, effortless body.

The stairs and the dancer — light, carefree — are suddenly connected, dance partners so in sync that they create, essentially, a new body. For Fred and Ginger, walking on air was walking on stairs. Don’t they just about lift off?

Stairs are never just stairs. Each step is a potential stage screaming for a dance — and often a dance of bravery and daring.

Part of the fun of dancing on stairs is giving up control: Are you riding the stairs or are they riding you? No matter how harrowing it feels, part of you has to relax to find balance, to reap the benefits.

Robinson wasn’t the first dancer to create a stair dance, but he was famous for his iterations, which lit up the vaudeville stage and beyond. Throughout the years, from one generation to the next …

… stair dances have just kept flowing — and overflowing — across the concert stage, in videos and film and, in miniature, on TikTok.

The stair shuffle dance challenge — as epitomized by the dancer Tuzelity — turned any old staircase into a jaunty, sideways ascent.

On stairs, an ordinary dance suddenly becomes one of courage and vulnerability, a marker of coordination and grace. Whether rising to the top or hopping down — or risking it all to skip a step — the dance sits on the precipice between precision and instability.

And for the dancer, a careful coordination is at play in which an articulate body must also remain loose. That’s what Joaquin Phoenix showed us in his famous staircase dance in “Joker.”

His body, agile and full of abandon, turns sinister as he marches, or descends, into madness. He slithers. Despite his glee, dancing isn’t really an act of joy; it’s an act of nihilism.

His body is louche and slippery, exposing his lack of fear and increasing entitlement. The more he dances, the more free he becomes — free of guilt, of pain, of anything that might get in his way. It’s frightening and breathtaking at once.

James Cagney danced on stairs, too. In this extended descent, he epitomizes the grace of balance.

He shifts his stride with steps that take up more air, becoming jauntier and lighter, until he springs into a sequence of sleek, low jumps …

… freezing in tiny scissor splits that demonstrate the length of his frame, the grace of his bearing, the groove in his beat.

As he performs the wing step, his feet really do look like wings.

For Astaire and Rogers, spinning while they rise, each on a separate gleaming staircase in “Swing Time” …

… or the ridiculously acrobatic, light as air Nicholas Brothers flying over each other in the splits in “Stormy Weather,” a stair dance is smooth sailing, showing the joy of being fearless. And spontaneous.

Even if a staircase sits tantalizingly in the background, a stair dance should seem like it comes out of nowhere, like the one with Moose in “Step Up 2.”

One second he’s standing; the next, he’s moving — his body transformed from flesh into an undulating, flowing ribbon.

But what are the roots? How did Robinson dream up his stair dance?

In a 1934 issue of The New Yorker, he told St. Clair McKelway about his inspiration: It had to do with the king and queen of England. “I dreamed I was getting to be a knight,” he said, “and I danced up the stairs to the throne, got my badge, and danced right down again.”

The sight of Robinson performing as the cheerful servant opposite the child with a mop of blonde curls is disconcerting.

If the world were good and fair, Robinson, dance royalty, would have lived in a castle with sparkling stairs — and Shirley Temple would have needed an appointment to dance one of their affable duets.

In their famous staircase dance in “The Little Colonel,” Robinson leads the way as he and Temple make their way up the steps holding hands. In this number, considered to be the first interracial dance on film, she matches his steps while glancing up at him in adoration.

Robinson guides her along, showing her — through the sound of his feet and the vibrations of his body — how to get inside the beat, how to trust that the rhythm of the step will override the peril of dancing on such a small, changeable surface.

To accidentally skip a step is to fall. To fall is to break the beat. Tripping is a menace. But it’s never just the feet toiling alone:

The body, like a set of stairs, is a structure — pitching forward in ascent and bouncing down on a descent as different rhythms converge.

Amateurs do it, too, especially those who take the subway — the everyday dancers of New York City. You see it in the panicked uphill sprint to catch a train before the doors close, and the carefree descent of breezy hops and swaying hips at the end of the day.

This dance of courage and risk on a staircase is not so different from how life feels now: seeking balance on unsteady terrain. You can do it! You can make those stairs sing.