It's Knot Magic

Here is an interesting article: ancient Incan strings/ropes may have been a form of writing.

Quoteth:

Yet, if centuries of scholarship are to be believed, the Inca, whose rule began 2,000 years after Homer, never figured out how to write. It's an enigma known as the Inca paradox, and for nearly 500 years it has stood as one of the great historical puzzles of the Americas. But now a Harvard anthropologist named Gary Urton may be close to untangling the mystery.