The site of the ancient city of Incahuasi, meaning “house of the Inca emperor,” sits in the hills above the Cañete River valley, about 100 miles south of the modern-day city of Lima, Peru. In the 15th and early 16th centuries, when the powerful Inca Empire extended throughout the Andes Mountains, from Ecuador to central Chile, Incahuasi served as a base for the Inca invasion of the southern Peruvian coast; today it is an important archaeological complex for researchers seeking insight into the life of the Incas. Recently, a team of archaeologists excavating an ancient storehouse there discovered an unexpected bounty: some 29 khipu, the mysterious knotted-string devices used by the Incas for various types of recordkeeping and communication.

The ancient Inca device known as the khipu consists of a series of knotted cotton or wool strings hung from a main cord, typically made from llama or alpaca hair. According to the Khipu Database Project, the word “khipu” comes from the Quechuan word for knot, and is used for both singular and plural forms of the noun. Some khipu have as many as 2,000 strings attached to the main cord. Each string may have several knots, the type and location of which convey different types of information.

Though researchers long ago figured out the basics of how the khipu works—how the knots represent numbers and the placement of the knots in the string represent mathematical operations such as addition and subtraction—they are still trying to figure out what other information may have been encoded within these “talking knots.” According to colonial-era documents, the Inca would use the devices in various ways, including sending messages via runners throughout their empire and recording historical narratives, calendar information and proof of land ownership.

Khipu at the Smithsonian National Museum. (Credit: BRENDAN SMIALOWSKI/AFP/Getty Images)
Khipu at the Smithsonian National Museum. (Credit: BRENDAN SMIALOWSKI/AFP/Getty Images)

Beginning in 2013, a team of archaeologists led by Alejandro Chu was excavating a storehouse in the Incahuasi complex when they discovered no fewer than 29 khipu. In the past, archaeologists had only found khipu in the graves of Inca scribes, who created and used the devices, and could derive little information about where or how they were used. The khipu at Incahuasi, however, were found in the very place where they were presumably used some 500 years ago—a storehouse used to house agricultural products such as corn, chili peppers, beans and peanuts. Now, Chu and his fellow researchers hope that by studying the khipu, and comparing them with others in a large existing database, they can learn more about their specific use and get a better idea of how they worked.

Leading khipu expert Gary Urton, who runs the Khipu Database Project at Dumbarton Oaks, an institute at Harvard University, and is studying the string-and-knot devices found at Incahuasi along with Chu. As Urton told the New York Times: “We can look at how the chili pepper khipu differs from the peanut khipu and from the corn khipu in terms of their color and other characteristics and we can build up a kind of sign vocabulary of how they were signifying this or that thing in their world.” Urton’s database currently includes all 870 khipu known to survive, along with detailed information—including configurations, colors and numerical values—about many of them.

As the Times reported, the 29 khipu are now being held at the Lima home of the archaeological conservator Patricia Landa, who painstakingly untangles and cleans each one in order to prepare it for examination by the researchers. When rolled up—the way in which they were transported for use during Inca times—a khipu bears a striking resemblance to a string mop. Though Chu believes even more khipu may be buried in the rest of the storeroom complex, which has yet to be excavated, the excavations have stopped due to lack of financing.