Researchers in the US believe they have come closer to solving a centuries-old mystery - by deciphering knotted string used by the ancient Incas.
The strings have baffled experts for centuries
Experts say one bunch of knots appears to identify a city, marking the first intelligible word from the extinct South American civilisation.
The coloured, knotted pieces of string, known as khipu, are believed to have been used for accounting information.
The researchers say the finding could unlock the meaning of other khipu.
Harvard University researchers Gary Urton and Carrie Brezine used computers to analyse 21 khipu.
They found a three-knot pattern in some of the strings which they believe identifies the bunch as coming from the city of Puruchuco, the site of an Inca palace.
"We hypothesize that the arrangement of three figure-eight knots at the start of these khipu represented the place identifier, or toponym, Puruchuco," they wrote in their report, published in the journal Science.
"We suggest that any khipu moving within the state administrative system bearing an initial arrangement of three figure-eight knots would have been immediately recognisable to Inca administrators as an account pertaining to the palace of Puruchuco."
Most experts agree the khipu represented an accounting system, but until now, no-one had been able to decipher them.
The researchers said their findings support what is already known about the Inca society.
"This work gives us some sense of how this complex information was compiled, manipulated, shared and archived in the Inca hierarchy," Mr Urton said in a statement quoted by Reuters news agency.
He said that 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.
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.