Historian Albrecht Classen got so tired of hearing people blithlely assert that chastity belts were ever a thing that he wrote The Medieval Chastity Belt: A Myth-Making Process, explaining how a 15th century hoax that appeared in a manuscript that also feature fart jokes and devices for making people invisible became canon.
From Sarah Laskow:
By the 16th century, chastity belts started showing up in more books and manuscripts, but Classen says that these were fanciful metaphors about male panic over infidelity, not literal depictions of women being locked up with steel girdles.
The physical belts you find in museums were almost never worn — they, too, were just gags. As the British Museum's commentary has it: "It is probable that the great majority of examples now existing were made in the eighteenth and nineteenth centuries as curiosities for the prurient, or as jokes for the tasteless."
Why has the myth of the chastity belt endured? It's hard to disprove an idea once it's firmly lodged in people's minds. As a result, the same scant information has managed to convince generations that medieval men locked up their wives' nether regions. Even the practical difficulties of such a device—as one historian wrote, "How could such a mechanism have been designed to permit the normal activities of urination, evacuation, menstruation, and hygiene, yet prevent both anal and vaginal penetration?"—have not dissuaded people from believing in chastity belts.
"People delight in delving into sex. They can say they only have a historical interest, but in reality they have a prurient interest," says Classen. "It's a fantasy."
For men, chastity belts are fantasy about female sexual appetites—women are so horny that only locking them up can keep them in check. For women, it's a fantasy about male cruelty and control. But for many people, it's simply a fantasy about sex. Even if chastity belts used to enforce medieval fidelity were not real, modern-day chastity belts, sold as fetish objects, definitely, definitely are.
Everything You've Heard About Chastity Belts Is a Lie [Sarah Laskow/Atlas Obscura]
The Medieval Chastity Belt: A Myth-Making Process [Albrecht Classen/Palgrave Macmillan]