An extraordinary piece of British history is going under the hammer. The BBC reports that a gilded copper plate taken from Oliver Cromwell’s coffin is to be auctioned at Sotheby’s London. The auction house estimates the one-of-a-kind artifact will sell for between £8,000 to £12,000 ($12,529 to $18,794).

The Latin inscription on the plaque says “Here is buried Oliver Protector of the Republic of England, Scotland and Ireland.” The plate was placed on Cromwell’s chest inside his coffin. The historian Earl Spencer explained “When he died … many people genuinely mourned him. The coffin plate was a mark of respect.”

A seminal figure in England’s civil war on the side of the Roundheads (Parliamentarians), Cromwell was one of the signatories of King Charles I’s death certificate before he was executed in 1649. Cromwell and the Roundheads believed King Charles I’s death was necessary to guarantee the transition of power back to parliament.

Cromwell briefly served as head of state from 1640 until his death in 1649, after which England became a monarchy once more. The new monarch, Charles II and his supporters, sought revenge against those responsible for his predecessor’s death.

According to Gabriel Heaton of Sotheby’s “People must have assumed that once the outer coffin was sealed the tablet would never be seen again. That turned out to be far from the case.” Shortly after Charles II took the throne, Cromwell’s dead body was exhumed and publicly cut to pieces.

Heaton admitted that “salesrooms are fond of the word unique,” but insisted that “in this case the term is justified.”