Since ancient times the practice of castrating pre-pubescent boys, and sometimes men, was thought to make them loyal servants, suitable for roles at the heart of many imperial courts. Some historians believe this began with human slaves who were treated in the same way as animals – as lesser beings to be managed and controlled – with no free choice.

The effects of castration on the male body – the loss of testosterone being the principal one – had a huge impact on how eunuchs have been viewed throughout history. Being unable to father children who could threaten lines of succession, certain eunuchs rose to power precisely because of their exclusive access to the inner workings of empires. Castrated men were also prized for their singing voices in 17th and 18th century Europe, as Dr Brianna Robertson-Kirkland explains.

Bridget Kendall discusses this painful episode with Norman Kutcher, Professor in the Department of History at the Maxwell School at Syracuse University in the US. He specialises in imperial Chinese history, and he’s the author of Eunuch and Emperor in the Great Age of Qing Rule; Dr Kathryn Reusch, conservation technician at the Denver Museum of Nature and Science, who's published widely on the topic of castration in relation to archaeological remains; and Shaun Tougher, Professor of Late Roman and Byzantine History at Cardiff University. He’s written many books and articles on eunuchs, including The Roman Castrati: Eunuchs in the Roman Empire.

Produced by Fiona Clampin for the BBC World Service.

(Photo: A group of court eunuchs in a Tang Dynasty mural from the tomb of Prince Zhanghuai (circa 618-907). Credit: Pictures From History/Universal Images Group via Getty Images)