The Antikythera Mechanism: Quest to Decode the Secret of the 2,000 Year Old Computer

The following is a guest blog post by Jo Marchant, author of Decoding the Heavens.

Main fragment of the Antikythera Mechanism (Photo: Jo Marchant)

The Antikythera mechanism is an ancient Greek clockwork computer that has lain at the bottom of the sea for two thousand years. I first came across it in late summer 2006, when a major paper describing its workings was due to appear in the science journal Nature, where I was on staff as an editor.

The story grabbed me immediately. If such a sophisticated device really existed, what did it do? Who could have made it? And why?

I travelled to Greece to see the remains of the device (on display in the National Archaeological Museum in Athens) and find out more about it. The modern part of its story begins in autumn 1900, when Captain Dimitrios Kontos and his crew of sponge divers were sailing home from their summer diving grounds of the coast of Tunisia. They were heading for the island of Symi in the eastern Mediterranean but were blown off course by a storm, and took shelter by a barren islet called Antikythera.

When the waters had calmed, one of the divers dropped down to look for sponges but soon emerged, gabbling about a heap of "dead, naked women" on the seabed. These turned out to be not corpses but statues, from one of the most spectacular shipwrecks ever discovered from the ancient world - a Roman ship carrying stolen Greek treasures west to Rome.

Among the salvaged hoard subsequently shipped to Athens was a piece of formless rock that no one noticed at first, until it cracked open, revealing bronze gearwheels, pointers, and tiny Greek inscriptions. It has taken more than a century of ingenious labour to fully decode this mechanism (during which it was largely ignored by mainstream historians) but scholars now know that it represents by far the most stunning scientific artefact that survives from antiquity. A sophisticated piece of machinery consisting of precisely cut dials, pointers and at least thirty interlocking gear wheels, nothing close to its complexity appears again in the historical record for more than a thousand years, until the development of astronomical clocks in medieval Europe.

Radiograph of the major fragments of the Antikythera Mechanism
(Images: Antikythera Mechanism Research PRoject)

The mechanism was encased in a wooden box, about the size of a squat dictionary, and operated by a handle on the side. Its purpose was to calculate the motions of celestial bodies. A large Zodiac dial on the front had several revolving pointers that represented the Sun, Moon and planets moving around the sky. Complex epicyclic gearing (in which wheels ride around on other wheels) was used to model the Greeks' latest astronomical theories, in order to display the variable speed of the Sun and Moon as seen from Earth as well as the wandering motions of the planets. Meanwhile on the back of the device were two spiral dials - one was a sophisticated 19-year calendar, developed to unify the motions of the Sun and the Moon, while the other displayed the timing of eclipses.

By turning the handle on the box you could make time pass forwards or backwards, to see the state of the cosmos today, tomorrow, last Tuesday or a hundred years in the future. Whoever owned this device must have felt like master of the heavens.

The mechanism dates to around 100 BC. It's not clear exactly where it was made, but the choices are limited as by this time the Romans had taken over most of the Mediterranean region, so Greek scientists weren't able to work freely. One possible source is Rhodes, where the shipwrecked vessel had stopped off shortly before its demise. Hipparchus, one of the greatest astronomers of the ancient world, lived on Rhodes in the second century BC, and his theory describing the varying speed of the Moon is beautifully captured within the mechanism's gearing. On the other hand, the calendar on the device incorporates month names that may be from Syracuse in Sicily, home to the famous mathematician Archimedes in the third century BC. Perhaps he first came up with the idea of using bronze gears to model the universe.

One question that has always intrigued me about the Antikythera mechanism is why the Greeks would have built such a machine. A clue may be found in the writings of Cicero, a Roman lawyer and author who lived in the first century BC. On a couple of occasions, he described "bronze spheres" that modelled the daily movements of the Sun, Moon and planets as seen from Earth. According to Cicero, Archimedes made one of these in the third century BC, while he attributed the other to a philosopher called Posidonius, who worked on Rhodes in the first century BC. Cicero gave no details of how these devices worked so historians haven't taken these stories very seriously - they figured the Greeks couldn't have been capable of building such complex machines. After all, until the sponge divers' discovery, archaeologists had never found a single gearwheel from the ancient world. But now that we know the Antikythera mechanism was exactly such a model, it seems likely that Cicero's account was accurate.

For both Cicero and Posidonius, these devices were of religious and philosophical importance. Cicero wrote about them to make the argument that just as it would be clear to anyone that they had a intelligent creator, so then did the universe itself. And Posidonius belonged to the Stoic school of philosophy, meaning that for him God was a divine life force that pervaded the entire universe. He would have seen astronomy and astronomical models as a way to understand and demonstrate the workings of the cosmos, and therefore to get closer to God.

The Greeks have often been dismissed by historians for wasting the technology they had on toys such as vending machines or automated puppet shows, instead of using it to tell the time or do useful work. Yet their most advanced creation, the Antikythera mechanism, was about demonstrating scientific principles and understanding the nature of the universe - and elevating one's spirit in the process. To me, that doesn't seem such a waste.

Recreation of the antikythera by Michael Wright, narrated by Jo [YouTube Link]

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Jo Marchant is a freelance journalist specializing in science and history, and author of Decoding the Heavens. In her book, Jo recounts the full story of the 100-year quest to understand the 2,000-year-old computer. She unearths a diverse cast of characters - from Archimedes to Jacques Cousteau - and explores the roots of modern technology in Greece, the Islamic world, and medieval Europe.

You can learn more about the Antikythera mechanism on Jo's website, her article at New Scientist, or on Wikipedia.

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