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.
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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