Knights who left for Crusades let their ladies wear a chastity belt to prevent them from having sexual intercourse. Fortunately it was still possible to go to the toilet.
Medieval chastity belts are made of iron and they have a lock, of course the knight kept the key with him.
The oldest known image of a chastity belt is from 1405, in Bellifortis by Konrad Keyser von Eichstatt, a book about the military techniques of that era.
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