In 1946, Harvard Law School Library paid $27.50 – around $450 (£333) today – for a 'copy' of the Magna Carta, a medieval document signed by King Edward I to outline the rights of the British people under common law.

The artefact was initially misattributed to King Edward III in 1327. However, 2025 analysis has shown it's actually an original from 1300, when the Magna Carta (which was first signed in 1215) was republished. Though the library has said it doesn't want to sell its version, it's been valued at millions of dollars.

Amazingly valuable treasures bought for very little money