U.S. researchers believe they became closer to the decipher o of knotted string used by the ancient Incas.
The dyed bunches of string have confused outsiders since Spanish conquerors first described them 500 years ago. Most experts agree they are ledgers of a sort but no one has been able to decipher them.
Now, Gary Urton and Carrie J. Brezine of Harvard University say they have found a three-knot pattern in some of khipu, Xinhua reports.
"We recently undertook a computer analysis of 21 khipu from the Inca administrative center of Puruchuco, on the central coast of Peru," they wrote in their report, published in the journal Science.
"Results indicate that this khipu archive exemplifies the way in which census and tribute data were synthesized, manipulated" they wrote.
The information is arranged among the khipus in a ranked pattern with three levels of authority. Information is passed between them by including the sum from a khipu in one level on a khipu representing a higher level, Scientific American says.
"Instructions of higher-level officials for lower-level ones would have moved via khipu, from the top of the hierarchy down." Commands for the society's large labor force could have been shared in this way, the authors suggest.
The researchers said their findings support what is already known about the Inca society.
The discovery could help researchers build up an inventory of place names, marking the first time khipu have been associated with words rather than numbers, BBC reports. Mr Urton said there are about 700 known khipu, two-thirds of which are arranged in a numerical pattern.
The others may hold the key to historical information and stories.
"We think those may be the narrative ones," Mr Urton said.