The Inca Empire ran the largest state in pre-Columbian America without an alphabet. Instead, administrators kept records on quipus — knotted cord devices that encoded numbers, and probably much more, in the way the knots were tied and the strings arranged. The quipu is one of the most unusual information systems any ancient civilisation produced.

1. No written alphabet.
Unlike Mesoamerican cultures to the north, the Inca did not develop a glyphic script. The quipu did the work that writing did elsewhere: census, tribute, grain storage, calendars.

2. How a quipu is built.
A primary cord carries hanging pendant strings of cotton or camelid fibre. Each pendant is tied with knots at specific heights, and the knot type (long knot, figure-eight, overhand) and position encodes meaning. Colours and ply direction add more variables.

3. Numbers in base ten.
The best-understood layer is numerical. Knot clusters at different heights represent units, tens, hundreds and thousands — a decimal system matching the one Spanish accountants ran into when they tried to tax Inca provinces.

4. Narrative quipus?
Scholars like Gary Urton (Harvard) and Sabine Hyland have argued some quipus encode non-numerical information: names, place-names, perhaps song. A 17th-century village quipu in San Juan de Collata, studied by Hyland in 2017, appears to contain phonetic logograms. The debate is active.

5. The quipucamayocs.
Reading a quipu was a specialist job. Each province kept quipucamayocs — professional record-keepers who could tie, store and read the cords. The Spanish chronicler Garcilaso de la Vega described them in detail; the office survived into the colonial period.

6. Oral tradition filled the rest.
Court genealogies, military history and cosmology travelled in the mouths of trained orators. The quipu anchored the numbers; oral performance carried the stories around them.

7. Why decipherment is hard.
There is no bilingual key — nothing like the Rosetta Stone — and the Spanish destroyed most of the archive. Only around 1,500 quipus survive worldwide.

8. What it tells us.
A state that governed 10 million people from Quito to Chile without an alphabet forces us to broaden what “literacy” means.

In short, the quipu is a record of a civilisation that built a different kind of writing — one knotted into cord rather than drawn on a surface — and we are still learning to read it.

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