A record made of cord
The Inca state, which called itself Tawantinsuyu and reached its height in the fifteenth and sixteenth centuries, had no known writing in the sense of a script for spoken language. It did have the khipu, in Spanish spelling quipu, a device made of cotton or camelid-fibre cords. A typical khipu has a main cord from which many thinner pendant cords hang, and some pendants carry further subsidiary cords. Knots tied along the pendants, together with the colour, the fibre and the way the cords were spun and attached, carried information.
Officials known in Spanish sources as quipucamayocs, a word usually glossed as khipu keepers, made and read them. Early writers, among them the Cusco-born chronicler Garcilaso de la Vega, whose Comentarios Reales appeared in 1609, described khipus as used for tallies of people, tribute and stored goods. Hundreds of khipus survive in museums and collections, and many are older than the Inca state itself, since earlier Andean cultures used cords as well.
How numbers sit on a cord
The numerical part of the khipu is the best understood. Numbers were written in a decimal, place-value system. Along a pendant cord, the position of a knot group indicates its place: groups closest to the free end stand for units, the next for tens, then hundreds and thousands, with the highest places nearest the main cord.
Three kinds of knot were used. A single overhand knot, tied in a cluster, stands for a digit in the tens place and above, with the number of knots in the cluster giving the digit. Units are shown differently: by a long knot with several turns, where the number of turns gives the digit from two to nine, and by a figure-eight knot for one. A place with no knots at all stands for zero, so a gap on the cord has numerical meaning. Pendants are laid out so that the same places line up across the khipu.
As a worked example, a pendant with three overhand knots in the hundreds place, two in the tens place and a long knot with four turns in the units place reads as 324. Place-value notation with an empty position for zero is the same principle as in the cuneiform place value of Babylon and the rod numerals of China, and it connects to the broader history of zero, though the Andean system arose on its own.
Checking sums
In the 1920s, the American mathematician Leland Locke showed that some pendant cords carry a total of the others. A summation cord hangs among the groups and holds a number equal to the sum of the numbers on a set of other cords. This looks like a built-in check, comparable to a column total in a ledger, and later researchers have found more complex relationships, including cords that repeat or summarise larger groups.
What else might a khipu hold?
Whether khipus recorded only numbers is a long-running question. Spanish chroniclers described them being used to remember histories, laws and lists, with an expert reciting from the cords, which suggests some narrative information may have been connected to them, perhaps as a memory aid for spoken text. What the cords themselves can encode is uncertain.
Colour, fibre, direction of the spin and the manner of tying a knot show regular variation, which some researchers think was meaningful. The anthropologist Gary Urton has argued that these features may form a coding system with a series of binary choices. Sabine Hyland has proposed, from work on a khipu preserved in the community of Collata in Peru, that some cords may record names in a phonetic way. These are hypotheses that have attracted both interest and doubt. No agreed decipherment of non-numerical khipus exists, and many scholars are cautious about claiming that they were a full writing system.
Why the debate persists
Several obstacles make progress slow. Most surviving khipus lack a known archaeological context, so there is little to tell us what an individual cord recorded. The Spanish colonial administration sometimes discouraged or destroyed khipus, and the knowledge of how to read them was passed on in person, so it was lost with the keepers. Much of what chroniclers wrote reflects their own assumptions as outsiders.
The khipu is also a reminder that systems for recording number developed independently: the Maya numerals of Mesoamerica, for example, were written in dots and bars, not knotted. For a reader, the practical lesson is that a khipu is better thought of as a flexible record-keeping technology than as a lost alphabet: for numbers it is clear and ingenious, and for everything else the honest answer is that scholars do not yet know.