Incas used knots for numbers, say researchers
Experts have found that collections of knotted strings, or “khipu”, were used by the Incas for number-based record keeping.
The strange stringy ledgers are thought to have kept track of workers and the jobs they were required to do for the government.
Since the Incas possessed no writing, khipu replaced the written records of other civilisations.
Clusters of khipu resemble a string mop with multiple knotted strings of different length and colour hanging from one horizontal string. Many have been found in Inca burial sites.
A number of theories have been suggested for their purpose, including their use as calendars.
The new evidence suggests at least some of them were used as “documents” in a bureaucratic accounting system.
How it worked is best understood in the context of Inca society.
The empire began in the 15th century and lasted only about a hundred years, until the Spanish arrived in South America in 1532.
The Inca emperor, or Sapa Inca, issued orders which were carried out by regional and local branches of government.
Male workers all had to spend a certain number of days a year working on government projects, such as farming state-owned land. Some of the food produced was sent back to the government as tribute.
Khipu appears to have been used by officials to keep track of workers and their tributes, and ensure the giant administrative machine ran smoothly.
The research, carried out by Prof Gary Urton and Carrie Brezine from Harvard University, was published in the journal Science. Prof Urton has argued khipu may also have been used as calendars.
