The mysterious Inca code of knotted strings

500 years ago, the Incas ruled the western half of South America with the help of a unique form of writing based on coloured and knotted strings. Researchers think they're getting closer to deciphering these strings, known as khipus. Guest: Professor Sabine Hyland, anthropologist from the University of St Andrews Producer: Sarah Allely Originally broadcast in June 2025.