Between the fifteenth and nineteenth centuries, European medical records filled with people convinced their bodies were made of glass. The most famous sufferer was a king of France; the last was a Bavarian princess who believed she had swallowed a grand piano. Tamara Sanderson traces the delusion as a cultural idiom — distress speaking in whatever language its era makes available.

  • Charles VI of France had iron rods sewn into his clothes after the Bal des Ardents of 1393, where four courtiers burned alive at his own masquerade — months after he had killed four of his own knights in a psychotic break and remembered none of it.
  • The casebooks are wonderfully strange: a man whose buttocks were windowpanes, a nobleman shaped like a glass pitcher who slept in straw, a patient who wanted to leap into a glazier’s furnace and emerge as a glass jug.
  • Cervantes turned the delusion into a kind of freedom in “El licenciado Vidriera” (1613): a man of glass has nothing left to conceal, so he speaks transparently — a pointed fable for Inquisition-era Spain.
  • Descartes invoked the glass man in the Meditations as the boundary of reason; Foucault and Derrida later fought over what that exclusion did to philosophy itself.
  • Why glass? Murano’s new, nearly invisible clear glass had just remade human sight — lenses, telescopes, microscopes — while the delusion traveled by contagion among the literate men who read the casebooks.
  • The last great case was a woman: Princess Alexandra Amalie of Bavaria (1826–1875), who turned sideways through palace doorways for twenty-five years to protect the glass piano she believed she carried.

A body made of glass cannot be sent to war, married off, or held to courtly expectation. Alexandra never married, never played — exemption dressed as affliction, and it did real work.

When glass became ordinary, the idiom faded (the last cases peter out in a Leiden hospital in the 1930s) and the terror found newer media: telegraph nerves, X-rays, and after the Great War, machines beaming thoughts into skulls. Madness, Sanderson suggests, is always contemporary.