Secret writing of the Incas
The Incas built an empire in the clouds. The largest one in the Americas. With an extensive network of paved roads complete with suspension bridges crafted from woven grass, it was an enigma as to why this sophisticated society had no written language.
They did have an intricate system of counting using colourful knotted cords as an abacus. It is now coming to light that these devices, called a khipu (pronounced key-poo), may be a hidden alphabet, encoding long-lost stories, myths and songs.
https://www.newscientist.com/article/mg23931972-600-we-thought-the-incas-couldnt-write-these-knots-change-everything/