Which people's quipu knots recorded numbers without writing?

A quipu is a bundle of knotted cords - a thick primary cord with dozens or hundreds of pendant cords hanging from it, spun from cotton or camelid fibre. The Inca ran an empire of some ten million people across three thousand kilometres with no writing system, and this is what they kept the accounts on: censuses, tribute owed, what was in which storehouse.

The numbers are genuinely positional and base ten. Knots are tied in clusters at fixed heights along a cord, the lowest cluster giving units and each cluster above it the next power of ten; a long knot with a number of turns gives digits two to nine, a figure-eight knot gives one, and zero is an empty space at the right height. Colour, the direction of the ply, and how a cord is attached all carry further meaning, which is why two quipus recording the same total need not look alike.

The specialists who made and read them were the khipukamayuq, the knot-keepers. Spanish authorities destroyed quipus as idolatrous objects and only about 1,400 survive. Some appear not to be numerical at all, and whether those encode language remains open; recent work matching surviving cords against colonial census documents has begun to prise a few of them open, which is the closest thing this field has to a Rosetta stone.