A three-dimensional script
The Inca Empire, or Tawantinsuyu, managed a territory of 12 million people without a conventional writing system. Instead, its administrators, the khipukamayuqs, used a recording technology called the khipu (or quipu). A khipu consists of a main horizontal cord, made from cotton or camelid fibers, with numerous smaller "pendant" cords hanging vertically. Information was encoded through a combination of factors: the type of fiber, the color of the strings, the direction the strings were spun and plied, and, most importantly, the knots tied into them.
About two-thirds of the approximately 1,400 khipus that survive today are understood to be numerical records. The system is based on a decimal, or base-10, structure. The position of a knot cluster on a pendant cord denotes its place value (ones, tens, hundreds, and so on) with the lowest value being farthest from the main cord. Three primary knot types were used: a figure-eight knot represented the number one, a long knot with two to nine turns stood for those corresponding values, and single overhand knots were used for tens and higher powers. Using this, khipukamayuqs recorded census data, tax obligations, military inventories, and calendrical information.
The silent library
Following the Spanish conquest which began in the 1530s, the use of khipus was suppressed. The Third Council of Lima, a meeting of the Catholic Church in 1582-83, ordered the complete destruction of khipus that documented non-Christian customs and rites, considering them idolatrous instruments. This act erased a vast library of Andean knowledge. While the numerical system is partially understood, the meaning of the remaining third of khipus, the so-called "narrative" khipus—is unknown.
Modern researchers are now applying new techniques to decipher these silent records. Harvard University's Khipu Database Project has digitized the details of over 900 khipus, enabling large-scale pattern analysis. A significant advance came when undergraduate Manny Medrano, working with professor Gary Urton, successfully matched six 17th-century khipus to a Spanish census document from the same period. Their work showed that cord colors and the way pendants were attached to the main cord corresponded to the social affiliations of the 132 individuals listed in the census. Other research focuses on a unique set of khipus from the village of Collata, which are believed to be narrative accounts of an 18th-century rebellion. These khipus contain 95 distinct combinations of fiber type, ply, and color, consistent with logosyllabic writing systems where symbols represent sounds and words.