1380-1415 French King Charles VI, commonly called ‘Charles the Mad,’ suffered from servere mental illness episodes through his life, including murdering his four of his own knights while in a psychosis, forgetting his name and that he was king, at times not recognizing his wife and kids, running through the halls of his castle until exhausted and screaming uncontrollably due to unseen enemies.

His most curious psychosis was that he at times thought he was made of glass. During these times, he would not let anyone touch him, was scared of furniture and even reinforced his clothes with metal rods to prevent accidental breakage.

Modern physicians and scholars have studied this so called ‘glass delusion.’ Though many experts today believe Charles suffered from schizophrenia or bipolar disorder, the glass delusion remains something of a mystery. There are few and unverified modern cases of people thinking they are made of glass, but there are numerous historical examples. A 1621 medical book by a prominent Oxford University professor described how mentally ill people were known to have thought they were made of glass, cork, feathers and lead, which the professor compared to psychiatric disorders of seeing demons and devils. 1800s Princess Alexandra of Bavaria, who had numerous neurosis and minor psychosis, thought she had swallowed a glass piano as a child and it was still inside her as an adult. Examples of people with the glass delusion appear in old literature, including a Miguel de Cervantes story where a poisoned law student falls into a long depression and believes he’s glass and a Rene Descartes philosophical essay where he uses an example of an insane person who thinks he’s glass.