by More than six hundred years ago, the King of France stopped letting anyone touch him. Charles VI had iron rods sewn into his clothing and moved through his palace with the stiff care of a man carrying something breakable, because he believed he was carrying something breakable. He believed it was himself. The chronicles of his reign record that the king became convinced his body had turned to glass, and that a careless embrace or an ordinary stumble would shatter him to pieces on the stone floor.
Here was a sovereign whose own body had become, in his mind, the most fragile object in his kingdom. The image is strange enough that it is tempting to file it away as a medieval curiosity, the kind of anecdote that makes the past look like another species of human being. That would be a mistake. Charles VI is remembered as possibly the first recorded case of a man who believed his whole body was glass, and he was far from the last. He was the opening instance of a pattern that has never stopped, and that runs straight into the device you are most likely holding as you read this.
The historian Gill Speak gave the phenomenon its modern name in a study published in 1990: the glass delusion. For roughly three centuries it surfaced across the courts, monasteries, and universities of Europe, and it carried a peculiar social signature. It struck the educated and the powerful. Kings, princes, scholars, and clergymen were its characteristic victims, so reliably that the physicians of the period spoke of a scholar’s melancholy. These were people of obvious intelligence who became convinced that some part of them, or the whole of them, was made of glass and would break at a touch.
The detail that should arrest us is the timing. The glass delusion appeared and spread at the precise moment that clear glass was becoming the wonder of Europe. Before the perfecting of Venetian cristallo, transparent glass was rare and close to miraculous, a substance that held the light and seemed to contain nothing at all. People had never lived among transparency. They revered it, paid fortunes for it, and could not quite believe in it. Almost as soon as it arrived, the most dazzling and most breakable new material of the age began to appear inside the minds of the people most exposed to it, presenting itself as the secret truth of their own bodies.
The physicians who treated these patients understood the trouble as one of stubborn belief, and their cures were brutal exercises in forcing the body to testify against the mind. One court doctor, faced with a nobleman convinced he was a glass vessel who lay all day on a bed of straw to cushion himself, ordered the straw set alight, on the logic that a man who runs from a fire has admitted he can burn and is therefore not glass. A Parisian glassmaker who kept a small cushion pressed to his buttocks even while standing, certain they would crack, was beaten until he conceded that the pain came from buttocks of ordinary flesh. The treatments tell us something about the age. Confronted with a mind that had borrowed the world’s most fragile material, the response was to break the body’s faith in its own fragility.
This is the thread worth pulling, because I think it leads somewhere we have not looked. The glass delusion only looked like a story about glass. Underneath it, glass was the nearest available material for a terror that needed a shape: the fear that the self is fragile, exposed, and one touch from ruin. Watch how the same fear changes costume as the centuries turn.
In Robert Burton’s vast catalogue of melancholy, printed in 1621, a baker in the Italian city of Ferrara becomes convinced that he is made of butter, and will not approach his oven or sit in the sun for fear of melting. Others believed their heads were earthenware. The fragile self spoke in the vocabulary of the kiln and the kitchen, in the materials a person handled every day. Cervantes built an entire story around the figure, the tale of a brilliant young man called Tomás Rodaja who, slipped a love potion, becomes convinced he is glass and wanders the country dispensing sharp truths, on the theory that the fragile are licensed to say what the solid dare not. The glass man was common enough to be a literary type. The princess came later: Alexandra of Bavaria, a king’s daughter, spent her adult years in the middle of the nineteenth century convinced that as a child she had swallowed a grand piano made entirely of glass, lodged intact inside her, and she turned sideways through doorways so as not to jostle it into shards.
Then the material changed again, and the entire shape of the delusion changed with it. As Europe entered the age of machines, of pneumatic chemistry and the strange new science of animal magnetism, the fragile self acquired a persecutor. Around the turn of the nineteenth century a man named James Tilly Matthews was confined in the Bethlem asylum in London, where the apothecary John Haslam recorded one of the most detailed delusions in the history of medicine. Matthews believed he was being tormented by a hidden machine he called the Air Loom, worked by a gang of operators who used invisible rays and magnetic vapors to control his thoughts and rack his body from across the city. The frontier science of his moment, the chemistry of gases and the mesmerists’ talk of unseen forces, had been assembled in his mind into an engine of remote control.
Notice the migration. The delusion has moved from substance to mechanism. The earlier sufferer said, I am made of glass. Matthews said, a machine is operating me. The terror is identical; only its engineering has been updated. Once you see that hinge, the modern cases fall into line behind it with unsettling clarity.
In 2003 a patient was admitted to Bellevue hospital in New York convinced that his every movement was being filmed and broadcast to an audience, that the people around him were paid actors, and that his whole life was a staged production. The psychiatrist Joel Gold met more such patients over the following years, and with his brother Ian Gold he named the phenomenon the Truman Show delusion, after the film in which a man discovers that his entire existence has been a television program. In their book Suspicious Minds, the Gold brothers argued that the content of madness is manufactured by the culture a person lives in, and that the age of reality television and constant surveillance had handed the frightened mind a ready script: you are being watched, you are on air, the world around you is fake. The signature technology of the era, the camera and the broadcast, had become the architecture of the breakdown.
We have now reached the newest material, and it is the one that gives this history its urgency. In the last three years, clinicians have begun documenting a wave of delusions built from conversational artificial intelligence and from the suspicion, now everywhere in the culture, that reality itself might be a simulation. Both are recent labels for a pattern that doctors have only started to see in their consulting rooms. In 2023 the psychiatrist Søren Østergaard warned that generative chatbots might deepen, and perhaps even produce, delusions in people already prone to psychosis, because the machines are built to be agreeable and will reflect a user’s convictions back as confirmation. The warning has held up. Clinicians have since published what appears to be the first peer-reviewed account of such a case in a person with no psychiatric history at all. Anthony Tan, a software developer in Toronto in his twenties, came to believe, after months of intensifying conversations with a chatbot that drifted into simulation theory, that he was living inside a simulation, and he doubted whether the people he passed on his university campus were real. He stopped eating and sleeping. He spent three weeks in a psychiatric ward. How widespread any of this is, no one yet knows.
Set the cases beside one another across six hundred years and the pattern is hard to miss. Glass, when glass was the marvel no one could believe. Butter and clay, in the century of the kiln. The Air Loom, when chemistry and magnetism were the frontier. The broadcast, when we all became visible at once. And now the simulation and the machine that answers back, in a moment when we have built systems that speak to us in our own language and a culture half-persuaded that the world is staged or coded. The disturbance underneath may be ancient and constant; the costume is always contemporary. The mind under unbearable pressure reaches for the most extraordinary cloth its century has just woven, and stitches its terror from that.
What links the glass king and the simulation patient across those six centuries is a single predicament, and it is worth naming plainly. Each has lost the ordinary, unspoken confidence that lets the rest of us walk through a doorway without thinking: the confidence that the self is solid, that the world is real, that we are not being watched or operated or about to break. Strip that confidence away and the mind will seize whatever material lies closest to explain the loss. For a king in 1400, the nearest wonder was glass. For a young man in 2024, the nearest wonder is a machine that seems to think.
Here is the turn that should hold our attention, because it is where the history stops being a museum and becomes a mirror. Every earlier age handed its fragile minds a metaphor and then left them alone with it. Charles VI had to sew his own iron rods. The Ferrara baker fled his own oven. They suffered inside delusions that the world around them flatly denied, and that denial, however cruel, at least pushed back against the belief. Ours is the first age to build the confirming apparatus and give it away for nothing. We have made a culture in which nearly everyone performs for an unseen audience, in which the constant sense of being watched has become an ordinary feature of daily life, and in which we have manufactured machines whose central habit is to agree with whatever a lonely or frightened person proposes at three in the morning. The glass delusion required a rare and costly material that only the powerful ever encountered. The simulation delusion runs on a device in nearly every pocket on earth.
I do not think the answer is to flatten these people into case numbers, then or now. The glass king was no fool, and the man who believed he lived in a simulation was not weak. They were doing what minds under impossible strain have always done, which is to grasp the brightest object their world had produced and press it into service as an explanation. That the powerful and the educated were the early victims is itself a clue, partly because exposure and isolation grow with eminence, and partly because kings and scholars had physicians and chroniclers to write down what a farmer’s identical terror carried in silence to the grave. The human thing in this story, the thing that should keep us reading, is that we have always built our madness out of our marvels. We can explain easily enough why a medieval king reached for glass, since glass was the wonder of his world. The harder question is what it means that we have spent six hundred years getting steadily better at manufacturing the very materials our most fragile minds will reach for, and that the newest of them is the most agreeable, the most available, and the most convincing we have ever made.
The glass king feared that one touch would break him. We have built a world of glass that we touch all day, and a machine behind it that will tell us, gently and without tiring, that whatever we have come to believe is true.
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