Around 1737, the Italian sculptor Francesco Bertos was hauled before the Inquisition. The charge: He had colluded with the Devil to produce his latest set of gravity-defying marble statues. According to his accusers, they were simply too impressive to have been carved by human hands.

The devilish sculptures in question have long since disappeared, but one glance at Bertos’ surviving corpus will show you where the Inquisitors were coming from. Bertos’ skill takes the stone to its very limit. Under his chisel, the wind-swept cloaks of nymphs are rendered almost translucent. Veins throb on flexed ankles. Torches blaze gouts of swirling fire. And all of this is rendered from blocks of brittle marble, no more than 30 inches high.

Associations with witchcraft have dogged artists for centuries. Take this rollicking tale from the sculptor Cellini’s memoirs, for instance: The great sculptor is almost half-dead with sickness when he discovers that one of his rivals has sabotaged the monumental bronze statue he’s been working on. So, he leaps up from his deathbed, dashes out into the thunderstorm that’s raging outside, and starts melting down his last set of pewter dishware to top off the mold. Somehow, the statue comes off perfectly, except for a single missing toe. No wonder that when Cellini announced his triumph the next day, his rival exclaimed that the sculptor “was no man, but of a certainty some powerful devil, since [he] had accomplished what no craft of the art could do.”

Sculptors past a certain point of skillfulness were suspicious. Maybe that’s because, in Renaissance philosophy, demons were considered to be sculptors of a sort. They were known to create illusions—nails pouring out of someone’s mouth, for instance—but theorists didn’t believe that demons were actually conjuring up the nails with magic. No, they were sculpting them out of whatever material was available: fog, smoke, cloud.

“One of the things demons can do,” wrote the Renaissance philosopher Francesco Cattani da Diacceto, “is operate bodies that appear to be men, or some sort of animal, the likeness of this body consisting in its figure and in its color. The figure is induced by means of local motion, just as painters, by means of brushes and other instruments, color their bodies.”

Demons and artists, it seems, pull from the same bag of tricks. They’re illusionists. They take the plain, humdrum matter of the world and transform it somehow, make it seem brighter, nobler, more wondrous, more terrifying. And here we have Bertos, taking blocks of solid stone and transforming them into something light and airy like a whipped-up meringue. Bertos’ sculptures weren’t monumental, they were ornamental. They were conversation pieces, meant to sit on some end table in a fabulously overwrought Rococo room. There, in their natural habitat, they would have been in perfect harmony with everything else: the fluffy, gilded rocaille decoration on the walls, the illusionistic fresco painted on the ceiling, probably featuring some fleshy, winged nymphs and cupids tumbling weightlessly through cotton-candy clouds.

With their writhing limbs and acrobatic postures, Bertos’ figures resemble the teetering human pyramids that used to be displayed on the Grand Canal of Venice during summer festivals. The people Bertos carves are equally acrobatic, equally precarious—and yet no evidence of athletic strain or effort shows in their bodies or expressions. His subjects are always graceful, elegant, even bizarrely blank-faced. They seem to float. It’s as if he’s captured them in the breathless moment of uplift, just before they all tumble down in a heap. Like those cartoon characters who don’t fall until they realize there’s nothing under them, Bertos’ sculptures are like freeze-frames, painstakingly chipped into blocks of Carrera marble. Maybe that is what made them seem so suspiciously magical in the eyes of the Inquisitors—the way they seem the blur the boundaries between the eternal and the momentary, between the heaviness of matter and the weightlessness of clouds.

In any case, Bertos was acquitted. He cleared himself of consorting with the devil by carving a new sculpture under the Inquisitors’ watchful eyes. He entitled the new piece The Triumph of Christianity, and inscribed it with a Latin motto: “Thus far it has been permitted to Francesco Bertos.” One sculptor went farther, however: Bertos’ follower, Agostino Fasolato, who carved the truly excessive tour-de-force, The Fall of the Rebel Angels. It’s a masterpiece: sixty figures fighting, swooping, pleading, breathing fire, all carved from a single block of marble. Yet for all that, it looks, as Herman Melville remarked in his tour diary of Italy, as “intricate as a heap of Vermicelli.”