Inca Tax Records Were Tied Up in Knots, Study Says

Stefan Lovgren
for National Geographic News
August 11, 2005
Known for its intricate textiles and spectacular architecture, the Inca Empire ranks among the world's great civilizations. Yet the ancient Inca apparently lacked a written language.

To record information, the ancient Inca used enigmatic devices called khipus, mop-like textiles. Made from cotton or animal hair, the objects consisted of multiple knotted strings hanging vertically from a single horizontal string.

Khipus were probably used for more than just recording numbers. Some experts say they may have been a medium for recording historical information—possibly as a form of writing.

Now a new study shows that khipus were used as documents in a sophisticated accounting system passed up through the Inca bureaucracy.

"They're quite complex, and there's a tremendous amount of information in them," said Gary Urton, a professor of pre-Columbian studies at Harvard University in Cambridge, Massachusetts. "They are beautifully structured to take care of what was … a hierarchical organization overseeing activities in the Inca Empire."

The study, by Urton and co-author Carrie Brezine, is published in tomorrow's issue of the academic journal Science. The researchers analyzed 21 khipus found in an urn under the floor of a house adjacent to the Inca palace of Puruchuco on the central coast of modern-day Peru.

Central Authority

Tribute in the form of a labor tax was imposed on subjects of the Inca Emipre, who were assigned to work a certain number of days each year on state projects.

Urton says the khipus that he analyzed, which were organized in a three-tier hierarchy, show how census and tribute data were assembled and transferred among different levels of authority within the Inca administrative system.

The khipus on the lowest level of the hierarchy may have represented contact between the khipu keeper and local laborers. While the top level probably represented contact between the palace of Puruchuco and a central authority.

"What we may have represented is that the khipus on top, containing the most aggregated data, came into the local palace as commands on the organization of activity on the local level," Urton said.

"And then that information was subdivided into the middle level and then further subdivided into the lower level."

Early Writing

In his 2003 book Signs of the Inka Khipu, Urton said the khipus may have been an early form of writing. Instead of using graphic signs for words, khipus may have used a sort of three-dimensional binary code, similar to the language of computers to represent information, Urton said.

One class of khipus was not mainly statistical in nature but may have represented poems, songs, histories, or genealogy. "This is an attempt to bring together information on khipu structure that had not been noticed or recognized by previous researchers," Urton said.

But no khipu narrative has been deciphered, and any interpretation of a writing system will be very hard to prove. While researchers know there is a connection between the system of writing numbers and the system of writing names and information, they can't yet prove it.

"We might read that a given khipu string contains the numerical value 256, but we don't know 256 of what," Urton said.

"I'm not saying [khipus could be] read like a phonetic alphabetic script. But we believe there's information there, in the forms of color or the directionality of the strings, that could be interpreted by someone knowledgeable in the system of recording to say, Oh, this is 256 workmen, or this is 256 days of work," Urton said.

Burial Site

Although it lasted for only a century, the Inca Empire, centered on the Andean mountain range, was the most extensive in the Americas before being destroyed by Spanish conquistadors in 1532.

The khipus were used throughout the reign of the empire. Earlier versions of the devices may have been used by pre-Inca people more than 500 years before the Spanish invasion.

The Spanish conquistadors destroyed most khipus they came across. Only about 700 khipus have been recovered, almost all from looted Inca tombs.

Khipus have a main horizontal cord from which thinner pendant strings hang. The Incas used three types of knots to tie these strings. The knots represented various numerical values.

For their new study, the researchers analyzed 21 khipus. Information about them was entered into a database constructed by Brezine, a mathematician and archaeology graduate student. The database allowed the team to compare and contrast values and information on the khipu strings.

The researchers found that 7 of the 21 khipus were related in a three-tier organization, believed to be an accounting hierarchy. Values on groups of khipus on the lower level were added up on strings of khipus at the next higher level.

"Until now all studies have involved looking at individual samples," Urton said. "Here, we are actually seeing the communication of information within a set of khipus … where the sum of values is not on the khipu itself but on another khipu. It's a communication event embedded there in the knots and strings of the khipu."

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