Jan Theiler works at the top of a mountain in Switzerland that has been made safe for novice skiers and walking tourists, and part of his job is to make sure it remains that way.

In the middle of the summer of 2017, a tower holding a ski lift above one of the intermediate trails had drifted slightly out of position, which was neither unexpected nor uncommon because both the tower and the trail are built on a glacier, and glaciers move. It does not matter that the ice has been tamed and groomed and that snow buses haul people across it to a monolith tottering at the edge: Beneath the surface snow, the glacier is constantly in motion, flexing and flowing with such force that anything on it, or under it, or in it, is going to move, too.

Usually the movements are imperceptible. Like stop-motion photography, the shifts and lurches aren't apparent until the frames are played back at speed. In 22 years working on the glacier, Theiler has seen the gradual but dramatic changes, the way it recedes year after year, the summer meltwater outpacing the winter snowfall. The slab creeps across a little less of Les Diablerets, a massif in the Alps of western Switzerland, each year, the blue-gray of the edges swirled like a tide pool on limestone slowly exposed by the seasons.

Theiler needs the big machine to nudge the tower back in place, the 34-ton Caterpillar parked near the bottom of the run. He drives one of the snow buses across the glacier, big treads churning through the midsummer slush. Ahead, in the light of the late afternoon, he sees a dark patch that hadn't been there a few days before.

He thinks it looks like mud.

The treads claw forward. No, it isn't mud. Too lumpy. Rocks, Theiler decides.

But how odd, he thinks, a clutch of black-brown rocks materializing at 2,600 meters, and tightly clustered, as if they'd been deliberately arranged.

He crawls closer in the bus. There is white space between some of the rocks, a background that makes the outlines clear. The first rock is long and narrow, until Theiler realizes it isn't a rock at all. It's an umbrella.

He gets out of the snow bus. He sees a bottle made of dark green glass, and it is lying across the toe of what appears to be a woman's boot. A few inches to the right, there is another boot, the bottom facing him so he can see the hobnails hammered into the sole. Long black appendages leak out of the boots, twisting down into the ice; they're covered in woven wool hose, so finely preserved he can make out the pattern.

There is another boot, too, a man's, sticking straight up, sole to the sky. And in the middle of those boots is a lump, which Theiler recognizes as a head. It is a deep, leathery brown, the color and texture of a ham left too long in the smokehouse, but he can tell it's a head because it has a face. The eyes are sunken and the cheeks are drawn, but it is obviously, unmistakably, a face.

The glacier where Theiler found the bodies is called Tsanfleuron, which in a mountain dialect translates to “field of flowers” and which, according to local legend, is what it used to be. There are several stories of how a meadow became a slab of ice—a miserly shepherd might have brought a curse upon the place, or the Devil himself might have frozen it out of spite—but the specific origin isn't the important part. Those tales were first told hundreds of years ago, when the western tip of Switzerland was poor and life was a struggle and there wasn't much to do at night except look at the stars and make up reasons to explain the apparently unexplainable. That not everyone heard the same story is not surprising.