Khipus served as recording devices in the Andes for over a millennium, using combinations of knots to represent numbers. These devices were essential for keeping track of inventory, such as corn, beans, and other provisions. Spanish accounts from colonial times claim that Inca khipus also encoded history, biographies, and letters. Chroniclers noted that Inca runners carried khipus as letters, and evidence suggests that the Inca composed khipu letters to maintain secrecy during rebellions against the Spanish. Fashioned from strings made of cotton, animal fibers, maguey, or other plants, and sometimes from human hair, khipus have varied in form and purpose throughout their 1000+ year history.
