Incan String Theory: If Knots Could Talk

We still don’t know how to de-code khipu, string-based information storage systems developed by the Inca, but they remain fascinating nonetheless.

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AsianScientist (Jul. 22, 2015) – Not having seen a movie in months, I was ready to take full advantage of the in-flight entertainment on a recent interminably long plane ride to Peru. Time passed a little bit faster in the company of Benedict Cumberbatch as Alan Turing in The Imitation Game, the story of how German Enigma machine codes were cracked during World War II.

Tied up in knots

Some cryptography skills may also come in handy for the traveler, especially when the language is foreign and the continent as vast and different as South America. Dusting off my rusty Spanish upon arrival in Lima, the first challenge was decoding verb conjugation.

“Good evening! We just eat here. We arrive in taxi very cheap, but now for to go back, it is very expensive. Please, you call new one?” is what I’m pretty sure I told the restaurant’s valet that first night, all forms of the past tense escaping me.

Several days later, we left cosmopolitan Lima for the former Incan capital of Cusco, perched in the Andes at 3,400 metres above sea level. Out in the surrounding Sacred Valley, our guide produced a brightly-colored bundle of yarn, disentangling it to reveal a series of knotted threads hanging off a horizontal string.

He explained that the Inca had used bundles like these, called khipu, to record information, encoding it in the positions, shapes, and colors of the knots. Only some 600 khipu remain in museums and private collections (most having been destroyed by the Spanish), so he’d made this one himself to show his clients.

Never underestimate the Inca

We were standing in front of the massive rock walls of Sacsayhuaman, and we’d later walk the Inca Trail to Machu Picchu, that perfectly-situated, expertly-crafted stone citadel in the clouds. It seemed odd: Why would the same civilization that built these enduring monuments limit themselves to communicating in such a primitive fashion, and on such perishable material?

If there’s one thing I learned in Peru, it’s this: Never underestimate the Inca. On the last day of the trip, I found myself staring at a huge khipu, framed and displayed in Lima’s Museo Larco. Its central cord was perhaps half a meter long, and radiating off it were dozens of hanging cords of different lengths and weaves, neatly dotted with knots of varying size and complexity. Once brightly colored but now faded to various shades of brown, it still managed to look like a work of art—one with a story to tell.

A closeup of the khipu at Museo Larco. Credit: Sim Shuzhen.
A closeup of the khipu at Museuo Larco. Credit: Sim Shuzhen.

It turns out that scholars have long puzzled over the Inca Paradox—the question of why such a technologically-advanced civilization never developed a system of writing. Khipu, their only system of recording information, were generally thought to be simply a means of representing numbers, for bookkeeping and census-taking purposes.

In recent years, however, more detailed analyses of the remaining khipu have been carried out, and some researchers now believe that they were also an early form of writing. Indeed, Spanish historical accounts indicate that native people considered khipu as narratives.

One account describes an encounter between Spanish travelers and an old man, who claimed that the khipu he was carrying contained a record of everything the conquistadors had done, “both the good and the bad.” (The Spanish burned the khipu and punished the man.) In another account, a Jesuit priest tells of a woman who used a khipu to write a confession of her entire life.

Cracking the code

But how could such detailed information be encoded in string? One theory is that the khipu are a sort of three-dimensional binary code. Researchers at Harvard University have compiled seven bits of binary information—for example, the direction of the twist in the cords, the color of the fibres, or whether the knots attaching the hanging cords to the primary one face backward or forward—that might help a reader interpret the khipu. For instance, one such bit could tell him to read the sequence as text and not as numbers; another could indicate that the text should be read as a name or an event, and so on.

Through an accumulation of these binary choices, layered on top of the basic sequences of knots, it’s estimated that the Inca would have had more than 1,500 units of information at their disposal. For comparison, Sumerian cuneiforms numbered fewer than 1,500, and Egyptian hieroglyphs fewer than 800.

Still, no narrative khipu has yet been decrypted, and the theory remains controversial and difficult to prove. Efforts continue: Mathematicians and cryptographers interrogating the khipu with pattern-recognition algorithms (one is similar to Google’s PageRank algorithm, and another to the suffix trees used in DNA sequence analysis) have identified sequences of knots that occur repeatedly, which could indicate words or phrases. To facilitate such analysis, the Harvard researchers have created an online khipu database, with entries on every minute detail of some 200 of the mysterious bundles.

Decoding the khipu may make us privy to the narratives, now hidden in plain sight, of a powerful empire that spanned 3,000 miles in its glory days. And perhaps also to excruciatingly detailed accounts of llama populations or corn harvests. Either way—magical or mundane—wouldn’t you like to know?

This article is from a monthly column called The Bug Report. Click here to see the other articles in this series.


Copyright: Asian Scientist Magazine; Photo: Sim Shuzhen.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Shuzhen received a PhD degree from the Johns Hopkins Bloomberg School of Public Health, USA, where she studied the immune response of mosquito vectors to dengue virus.

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