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Knotted strings, not written records, for the ancient Inkans

A larger khipu, not one of the group analyzed in this study.
Click here for a high resolution photograph.

For decades, archeologists exploring the remains of the Inkan empire, an ancient civilization in western South America, have found mysterious clusters of knotted strings called "khipu." Because they are so common, khipu appear to be quite important, but what do they mean and what were they used for?

The Inkas didn't have a written language, but the khipu seem to be part of a system of number-related record keeping. A new study shows that the khipu may have used to keep track of workers and the jobs they were required to do for the government.

One of the knotted string objects called "khipu," used for record-keeping in the Inka empire.
Click here for a high resolution photograph.

Clusters of khipu look kind of like a string mop, but they're actually much more organized than a mop. A single khipu has multiple knotted strings, in different colors, all hanging vertically from one horizontal string.

Each knot, depending on what type of knot it is and where it's placed represents some kind of number.

Gary Urton and Carrie Brezine of Harvard University studied a set of 21 khipu from the Inkan administrative center of Puruchuco, which is on the central coast of Peru. They describe their findings in the 12 August issue of the journal Science.

To understand what they learned about the Khipu, it helps to know a little more about Inkan society. The empire began in the 15th century and lasted only about a hundred years, when the European conquerors arrived, in 1532. The Inka emperor was called the Sapa Inca, and his orders were carried out by regional and local branches of government. Male workers all had to spend a certain number of days of the year working on government projects, such as farming land owned by the government. Then, the food they produced, say bushels of corn, was sent back to the government as a "tribute," or tax.

Urton and Brezine identified different categories in seven of the 21 khipu they studied. All the khipu in this group of seven were used to record the numbers of workers and the tributes they produced. The lowest level of khipu, probably kept by officials at the most local branches of government, had the most detail. Local officials could then send the khipu up to higher branches of government to report on local activities. Or, higher branches of government could send khipu down to local branches. These khipu might contain orders for work projects or tax collection.

Many questions remain to be answered, such as how the khipu-keepers recorded the identities of objects -- people, animals, produce, manufactured goods, etc. -- in addition to numerical values in the beautiful knotted-strings of their khipu.