It's often said that the indigenous people of South America never developed a system of writing.

But this isn't entirely true. In fact, they created a unique and complex system of notation based on the tying of knots, known as quipu, which remain undeciphered to this day.

The quipu were usually made from string, spun from cotton fibers, or the fleece of camelid animals like the alpaca and llama.

The cords stored information with knots tied in vast assemblages of string, sometimes containing thousands of threads.

In some analysed quipu, the combinations of thread length, colour, knot type and knot position allow for up to 95 possible combinations, which could represent numbers, symbols or even sounds.

The Inca people used them for collecting data and keeping records, monitoring taxes, conducting censuses, keeping track of dates, and for military organization, all with immense success.

One early European eyewitness Hernando Pizarro records one early sighting of these quipu.

In fact, these quipu were the only system of notation used to administrate the Incas’ society, a vast stretch of land the same size as the Western Roman empire in Europe, containing more than 10 million people – all of which operated without a single word being written down.