The 2,000 Year Old Computer That Shouldn’t Exist: The Antikythera Mechanism

“The mechanism is like a great astronomical clock without an escapement.” - Derek J. de Solla Price

In 1900, a group of Greek sponge divers sheltering from bad weather near the tiny island of Antikythera decided to explore beneath the water. Around 50 metres below the surface they discovered the remains of an ancient shipwreck that had been lying at the bottom of the Mediterranean for almost 2,000 years. The wreck contained bronze statues, marble sculptures, jewellery, coins and numerous other treasures from the ancient world. Among these spectacular objects was a badly corroded lump of bronze that initially looked considerably less impressive. Nobody looking at it could have imagined that inside the green and brown mass were dozens of interlocking gears belonging to a machine more sophisticated than anything else known to have survived from antiquity.

The recovery operation was extremely dangerous. The sponge divers descended in heavy diving suits supplied with air from the surface, working at depths where even a small mistake could prove fatal. One diver lost his life during the excavation and others suffered serious injuries, but enormous quantities of ancient material were eventually brought to the surface. Understandably, the statues attracted most of the attention. A corroded lump of bronze sitting among them was unlikely to compete with beautifully preserved works of Greek art, and for a time the object remained something of a curiosity rather than the centrepiece of the discovery.

That changed when researchers noticed something inside one of the fragments that should not have been there. Visible through the corrosion were the unmistakable teeth of a bronze gear wheel. Other fragments contained more gears, circular scales, pointers and tiny inscriptions written in ancient Greek. This was clearly not part of a statue or an ordinary piece of equipment. Somebody in the ancient world had constructed a complicated mechanical machine using dozens of precisely organised bronze components. What the sponge divers had accidentally pulled from the seabed would eventually become known as the Antikythera Mechanism and is now widely described as the oldest known analogue computer.

The mechanism appears to have been constructed towards the end of the second century BC, although exactly where it was made and who designed it remain uncertain. Only around one third of the original machine survives, divided into dozens of damaged fragments. Thirty bronze gears have survived, although the complete device contained more. Trying to reconstruct it is therefore rather like finding part of a complicated mechanical watch after it has spent two millennia underwater and then being asked not only to repair it but to explain what its missing parts once did. Remarkably, after more than a century of investigation, researchers have managed to do exactly that with much of the machine.

The Antikythera Mechanism was essentially an astronomical calculator. Turning the mechanism caused its gears and pointers to reproduce important astronomical cycles. It could display information relating to the Sun and Moon, track calendars and predict the approximate occurrence of solar and lunar eclipses. Its inscriptions also refer to the five planets visible to the naked eye and known to Greek astronomers: Mercury, Venus, Mars, Jupiter and Saturn. Modern researchers continue to debate precisely how every part of the missing front display operated, but it is clear that the machine attempted to reduce the movements of the heavens to a system of bronze gears. An ancient Greek user could therefore manipulate a mechanical device and receive information about celestial events taking place months or even years in the future.

One of the most impressive features was its ability to deal with the Moon. The Moon does not appear to move across the sky at a perfectly constant speed, something ancient Greek astronomers had already recognised. The designer of the mechanism managed to reproduce this irregular movement mechanically through an ingenious arrangement of gears. Modern investigations have shown that the machine incorporated astronomical ideas associated with the work of Hipparchus, one of the greatest astronomers of the ancient world. Whoever constructed the mechanism was therefore not merely an accomplished metalworker. They had access to advanced astronomical and mathematical knowledge and possessed the engineering ability to turn those ideas into moving pieces of bronze.

The rear of the machine was equally remarkable. One dial represented the Metonic cycle, a period of 19 years in which 235 lunar months correspond closely with 19 solar years. Another represented the Saros cycle, a period of 223 lunar months that ancient astronomers could use to anticipate the recurrence of eclipses. The mechanism even incorporated a four-year cycle connected with important Greek athletic festivals, including the Olympic Games. Somewhere in the ancient Mediterranean, somebody had therefore constructed a machine capable of tracking astronomical cycles, predicting eclipses and reminding its owner when major sporting competitions were approaching. In modern language, it was part computer, part astronomical model, part calendar and, rather unexpectedly, part Olympic Games reminder.

This is where the Antikythera Mechanism becomes particularly uncomfortable for our traditional understanding of technological history. We naturally imagine technological development as a staircase. Ancient civilisations build relatively simple machines, medieval engineers improve upon them, Renaissance inventors become more sophisticated and eventually modern technology emerges. The Antikythera Mechanism does not fit neatly onto that staircase. Its intricate system of gears represents a level of mechanical sophistication for which we possess no comparable surviving object for more than a thousand years afterwards. Science historian Derek J. de Solla Price recognised this decades ago when he compared the mechanism to an astronomical clock and a mechanical analogue computer.

The obvious question is therefore where all the other machines are. Technology this complicated is unlikely to have appeared spontaneously in one workshop before immediately disappearing again. Somebody needed to know how to cut the gears. Somebody needed to calculate their ratios. Astronomers had to provide the information that the machine represented, while craftsmen needed sufficient experience to fit everything together inside a relatively small case. There must have been earlier experiments, failed attempts and probably other successful devices, yet almost none have survived. The Antikythera Mechanism appears to us as a technological orphan, possessing extraordinary sophistication but with no surviving parents and very few obvious descendants.

Ancient literature provides tantalising hints that such machines may once have been more common. The Roman writer Cicero described mechanical models of the heavens and discussed devices associated with the Greek mathematician Archimedes. According to these accounts, machines existed that could reproduce the movements of the Sun, Moon and planets. Archimedes himself died in 212 BC, probably decades before the Antikythera Mechanism was constructed, so there is no evidence that he personally built it. Nevertheless, the descriptions suggest that ancient Greek engineers possessed a tradition of mechanical astronomy of which the Antikythera Mechanism may simply be the only substantial survivor.

Other clues have led researchers towards places such as Rhodes, Corinth and Syracuse, all important centres of Greek learning at different times. Hipparchus was associated with Rhodes, while Syracuse immediately raises the tantalising connection with Archimedes. Inscriptions deciphered from the mechanism have also provided clues about the calendar tradition used by its makers. Despite more than a century of investigation, however, nobody has been able to identify the person who designed it. One of the most sophisticated engineers of the ancient world therefore remains completely anonymous.

For decades, the greatest obstacle facing researchers was that much of the important information was hidden inside the corroded fragments. Ordinary examination could reveal some gears and letters but much of the mechanism remained inaccessible without destroying it. Modern technology eventually came to the rescue of ancient technology. High-resolution imaging and three-dimensional X-ray tomography allowed researchers to look inside the fragments and examine gears and inscriptions that had been concealed for roughly 2,000 years. Thousands of previously unread characters gradually became visible, transforming our understanding of the machine.

The most remarkable discovery was that many of these inscriptions effectively functioned as instructions. Parts of the mechanism contained explanations relating to its displays and astronomical functions. The ancient machine had, in a sense, survived together with fragments of its own instruction manual. Researchers could combine these inscriptions with X-ray images of the surviving gears and begin reverse-engineering a machine created by an unknown craftsman more than two millennia earlier. Studies published in the 2000s confirmed its ability to model lunar motion and predict eclipses, while later research demonstrated its connection with the cycle of the ancient Greek games. More recent reconstructions have attempted to recreate the missing front section and show how the planets may have been displayed.

Despite everything we have learned, the machine continues to keep some of its secrets. Most of the original mechanism is gone and different researchers continue to disagree over aspects of its reconstruction. We do not know who commissioned it, who owned it or exactly why it was being transported aboard the ship when it sank. It may have belonged to a wealthy individual, an astronomer, a school or somebody interested in displaying the extraordinary achievements of Greek science. Considering the valuable statues and other objects travelling aboard the same vessel, it certainly does not appear to have been an ordinary household appliance.

The greatest mystery surrounding the Antikythera Mechanism may therefore not be how it worked but how much ancient technology has disappeared with nothing left behind. Bronze was valuable and could easily be melted down and reused. Machines broke, buildings burned, cities were destroyed and metal objects were recycled. Had the ship carrying the Antikythera Mechanism safely reached its destination, the machine might eventually have been dismantled or melted down like countless other ancient objects. Ironically, the disaster that sent the ship and its passengers to the bottom of the Mediterranean may be the only reason we know this technology existed at all.

This creates an intriguing possibility. The Antikythera Mechanism may not have been particularly unique when it was constructed. There may once have been workshops producing similar astronomical machines and craftsmen capable of repairing them. Other examples may have sat in the homes of wealthy Greeks or Romans, been used by astronomers or displayed to demonstrate the remarkable order of the heavens. Almost all of them could simply have disappeared during the following two thousand years. The Antikythera Mechanism may be extraordinary not because it was the only machine of its kind, but because it was the only one unfortunate enough to sink and fortunate enough to survive.

Today, its damaged fragments are preserved in the National Archaeological Museum in Athens. Visually, they are nowhere near as impressive as the beautiful bronze and marble statues recovered from the same wreck. To somebody unaware of their significance, they look like little more than pieces of heavily corroded metal. Yet inside those fragments are the remains of an ancient machine capable of predicting eclipses, modelling astronomical cycles and mechanically representing a Greek understanding of the heavens at a level of sophistication that would disappear from the surviving technological record for centuries.

More than 2,000 years ago, an unknown Greek engineer looked towards the sky and decided that the movements of the heavens could be recreated using mathematics and bronze gears. We have spent more than a century trying to understand the machine that person left behind, and modern computers and X-ray technology have finally allowed us to decipher much of what they achieved.

We know how many of their gears worked, we know much of the astronomy they understood and we can now build functioning reconstructions of their machine. The one thing the Antikythera Mechanism has never revealed is perhaps the simplest detail of all: the name of the person clever enough to build it.