#15: Quipu–Knot-Based Data Recording in the Inca Empire
Quipus were intricate knotted cord devices used by the Inca to record numerical data, tax obligations, and even military and census information, serving as a complex record-keeping system. The quipu system employed a decimal positional system with knots tied in various patterns, using the color, order, and number of knots to encode different types of data.
