by Decoding the Heavens- Solving the Mystery of the World's First Computer (retail) (epub)
When the omens were first compiled, the astronomers probably observed each celestial sign directly, then enacted the appropriate ritual. But after a few centuries of keeping meticulous records they started to establish patterns in the recurrence of different heavenly events, until eventually they didn’t need to see them at all and could predict them in advance, even the seemingly aimless motions of the planets.
Babylonia and Assyria became part of the Greek world in the fourth century BC when they were conquered by Alexander the Great. After that there were no indigenous kings for astronomers to report to, but their cults remained an important part of life. Babylon gradually emptied as the Greek rulers moved the locals to their new capital Seleucus on the Tigris, but a small group of priests held out at the city’s temple complex. For another couple of hundred years these lonely astronomers carried on observing the skies and doggedly tended statues of their gods as if they were living beings – feeding them, clothing them and parading them around the empty temple.
Isolated snippets of information from the Babylonian astronomers had already started to filter through to the Greeks. But during the second century BC Hipparchus took this much further, basing large sections of his work on their data. We know from Ptolemy that Hipparchus relied on a list of eclipse observations reaching back centuries and that he converted long stretches of planetary observations into the Egyptian calendar (the same one represented on the front of the Antikythera mechanism), so that they were more convenient for Greek astronomers to use. The Babylonians were the only ones we know of who had such data. The historian of astronomy Gerald Toomer, who studied Ptolemy’s writings extensively, concluded that Hipparchus must have travelled to the temple in Babylon himself and worked with the last astronomers there to extract the information that he needed from the old tablets.
Seeing the accuracy that these priests achieved is probably what inspired Hipparchus to strive for similar precision in the geometrical models that his peers were throwing about at the time. He used the Babylonian data to derive numbers for the models and in doing so transformed Greek astronomy from a largely theoretical science into a practical, predictive one. The reason that Hipparchus is such an important figure is because in him two long traditions of astronomy became one. When Ptolemy later built on Hipparchus’ work it set the foundation for all of western astronomy until Copernicus and Kepler kicked out the geocentric view and reinstated the Sun at the centre of things in the sixteenth and seventeenth centuries.
It is tempting to think that the Antikythera mechanism – a machine that also embodies both the geometrical circles of the Greeks and the precise arithmetic of the Babylonians – might have had something to do with Hipparchus. If you take the very earliest end of the date range suggested by the inscriptions, then it’s just possible that he was still alive on Rhodes when the mechanism was built. So, if the device was made by Hipparchus or his followers, what would they have used it for?
The mechanism displayed the state of the skies at any chosen moment in time. It incorporated sophisticated astronomy theory and was clearly made by someone who cared a lot about making it as accurate as possible. But it wasn’t an astronomer’s workshop tool. There’s no obvious way in which the device could have been used to make observations. And it was covered in idiot-proof inscriptions, so it probably wasn’t intended for use by someone with specialist knowledge.
One possible purpose is to cast horoscopes. The art of astrology – the idea that a person’s fate depends on the configuration of stars and planets at the time of their birth – was just becoming popular in the Hellenistic world at the time that the Antikythera mechanism was made. A key requirement for practising astrology is being able to work out what the stars and planets were doing when a person was born (otherwise you’d always need an astronomer on hand at the birth to note it all down just as the baby pops out). The Greeks couldn’t do this for the planets before the second century BC. But when Hipparchus brought back the Babylonian’s arithmetical models of the planets’ motion – making it possible to use written tables to extrapolate backwards or forwards in time – astrology took off. If the Antikythera mechanism showed the planets, it would have been the ultimate luxury gadget for checking the state of the skies at any desired moment, something wealthy clients (including the Romans, who loved astrology) would have paid a lot of money for.
We don’t have any writings from Hipparchus on astrology, but he seems to have advocated the idea – the heavens governed the seasons and the tides, after all, so why shouldn’t they influence other things on Earth too? For example, the Roman historian Pliny wrote in the first century AD about astrology’s great debt to Hipparchus, saying that he ‘can never be sufficiently praised, no one having done more to prove that man is related to the stars and that our souls are part of heaven’.
There is another big name from Rhodes, however, who suggests a rather different interpretation of the Antikythera mechanism. Suspect number two is a philosopher called Posidonius, and he was working on the island at exactly the time our clockwork box set off on its last journey. He was born in 135 BC to a Greek family in Apamea, a Roman city on the river Orontes in Syria. He settled in Rhodes around 95 BC, where he founded a school. He was nicknamed ‘the champion’ and seems to have been universally recognised as one of the most wise and learned men in the Hellenistic world. Posidonius was also a senior politician – he was president of Rhodes for one six-month term, and he travelled to Rome as Rhodes’ ambassador in 87–86 BC, around the time that Sulla was smashing his way through Athens. He made friends with some key Roman figures there, including Pompey, the up-and-coming general. Pompey visited Posidonius on Rhodes in 66 BC, just before he set off to take on the stubborn king Mithridates (he asked the teacher for advice, who replied diplomatically: ‘Be ever the best’) and again on his triumphant return. According to Pliny, Pompey stopped his assistant from striking on Posidonius’s door, and instead ‘the man to whom the East had bowed in submission bowed his standard before the door of learning’.
As if that wasn’t enough, Posidonius excelled in geography and science too. He travelled widely before settling in Rhodes – to Greece, Spain, Africa, Italy and most famously to the Celtic lands of Gaul, in the decades before the Romans took over. He wrote vivid descriptions of the wild and violent goings on he found there, including how the warriors would hang the severed heads of their enemies in doorways when they got home (something the scholarly Posidonius found nauseating at first, though he got used to it after a while), and how at feasts, which often ended up in rowdy fights to the death, a man would sometimes take pledges of gold or wine, distribute it to his friends, then lie face up on his shield so that someone could slit his throat with a sword for the general amusement of the party.
On his travels he observed the regular patterns of the tides, and theorised that they were caused by the motions of the Moon. And back in Rhodes he used astronomical observations to estimate the distance and size of the Sun. He was a key member of the Stoic school of philosophy and his interest in the heavens came very much from his Stoic world view, which interpreted the cosmos as a single organism, infused with a divine, intelligent life force that gave it form and direction. Could Posidonius have been behind the Antikythera mechanism?
If so, it was probably meant not as an astrological tool, but as a philosophical or religious demonstration of the workings of the heavens. We have an important piece of evidence to support this idea, from the Roman lawyer and politician Cicero. He spent time on Rhodes when he was a young man in the early 70s BC, just a few years before the Antikythera ship sailed. (His trip was possibly motivated by a desire to keep out of General Sulla’s way, because Cicero had just implicated an associate of his in a murder case.) While in Rhodes, Cicero studied with Posidonius and later wrote about an instrument ‘recently constructed by our friend Posidonius, which at each revolution reproduces the same motions of the Sun, the Moon and the five planets that take place in the heavens each day and night’.
Cicero
went on to ask: ‘Suppose someone carried this to Scythia or to Britain. Surely no one in those barbaric regions would doubt that the orrery had been constructed by a rational process?’ His point was that just as the sphere had an intelligent creator, so did the universe. Posidonius believed more in a guiding life force than a distinct creator, but to philosophers of all persuasions a machine that modelled the workings of the solar system would have been a powerful reassurance of the order or purpose that lay behind the nature of things.
Despite having a name that meant ‘chickpea’ (thanks to an ancestor whose nose apparently resembled one), Cicero was pretty much the leading intelligence in Rome for his time. He was one of the first people to write about philosophy in Latin – his mission was to make Greek teachings available to the Roman reading public. But his political judgement was often flawed. While trying to play in Rome’s big league, for instance, he got caught between the generals vying for leadership (including Julius Caesar and Pompey) and in the end was hunted down and killed by Mark Anthony’s men in 43 BC.
Although Cicero’s writings are generally trusted, scholars throughout history took his account of Posidonius’ device with a large pinch of salt. Cicero had no scientific training and he provided no technical description of how the instrument worked. To simulate the movements of the planets would have taken a sophisticated system of gears, which was thought way beyond the craftsmen of the time, so the whole things sounded pretty unlikely. After all, he could have made the story up just to illustrate a point. However, the Antikythera fragments prove that the technology did exist and suggest that Cicero’s description can be taken seriously after all. Perhaps our mechanism was commissioned by Posidonius as a demonstration piece for all who came to study there, or as a prized gift for an important visitor, such as Pompey.
Modelling the heavens with geared devices ran alongside a parallel philosophical tradition of modelling living creatures: people, animals and birds. These didn’t use gearwheels, instead they were powered by steam, hot air and water. The tradition seems to have started with the engineer Ctesibius, working in Alexandria in the third century BC. He was a big specialist in water clocks, many of which included automated figures. The Tower of the Winds, reconstructed by Price according to one of Ctesibius’s designs, may also have incorporated little puppets that moved alongside the turning disc of the heavens.
The engineer Hero, who worked in Alexandria in the first century AD, built on Ctesibius’s work. He invented the first steam engine, as well as the first vending machine, which dispensed holy water, and also the first wind-operated organ. He created all sorts of wondrous mechanical shows, both for theatres and for temples. In one example, a platform carrying a figure of Bacchus (the god of wine and intoxication) moved forwards to an altar causing a flame to burst forth, while wine flowed from his cup and automated figures danced around the temple to the sound of drums and cymbals.
Historians have often scoffed at the Greeks for wasting their technology on toys rather than doing anything useful with it. If they had the steam engine why not use it to do work? Looking at the Antikythera mechanism we might also ask: if they had clockwork, why not build clocks? Many centuries later, in Europe, such technology prompted the Industrial Revolution, ushering in our automated modern world. Why did it not do the same for the Greeks?
In the 1960s and 70s the popular view was that because the Greeks had slaves to do manual labour there was no incentive to develop technology to replace them. That argument has now fallen out of fashion and most experts will tell you the answer is more complicated than that. Even in slave-owning societies machines can benefit owners by allowing slaves to do more work than they did before – such as when the cotton gin caught on in the plantations of the American Deep South at the end of the eighteenth century.
It probably has more to do with what the Greeks would have regarded as useful. Models of people and animals, like those of the cosmos, affirmed the idea of a divine order. The Greeks didn’t think that real creatures ran on steam, just as they didn’t think the planets were powered by cogs, but the fact that they clearly had a designer argued implicitly that the same was true for the universe. Gadgets like Hero’s also went beyond that general principle to demonstrate basic physical laws in pneumatics and hydraulics.
Take Hero’s famous steam engine, for example. This consisted of an airtight ball-shaped chamber mounted on to a horizontal metal axis. The axis was also a pipe that fed steam into the sphere as a water chamber beneath was heated, and the only way that the steam could escape was through two bent nozzles, one on either side of the chamber. This set-up forced the steam out of the ball perpendicular to its axis, causing it to spin around at high speed.
There is no obvious way that this contraption could be made to do useful work, and it has often been derided as a mere toy. But a more recent interpretation is that Hero intended his engine to demonstrate a particular physical principle. Several centuries earlier the philosopher Aristotle had argued that for any animal to move it must be supported on something ‘unmoved and resisting’. A walking man pushes against the earth, for example, and a fish pushes against the sea as it swims. But a man in a boat won’t go anywhere however hard he pushes against the inside of his vessel. Aristotle also applied this principle to the spheres that he believed carried the celestial bodies. He argued that their circular motions were passed on to them by the outermost sphere, which in turn derived its motion from the ‘unmoved mover’, in other words, God.
It has been suggested that Hero built his steam engine to disprove Aristotle’s theory, as the force of its motion derived from within the sphere, with no need for an external source. As with the Antikythera mechanism, this ‘toy’ was far from trivial. The aim was to advance a philosophical principle, to aid understanding of the universe and improve oneself in the process. To what better use could technology be put?
There was a practical side to this as well. As a member of the relatively small ruling elite in the Hellenistic world, the most useful thing you could do in terms of gaining power and prestige was to impress your peers. You did that not by timing an hour more accurately or ploughing a field faster, but by demonstrating what you knew.
This wasn’t about education so much as inspiring awe and wonder. In many of Hero’s devices, as with the Tower of the Winds, the working mechanisms were hidden – it was all about putting on a show.
For example, Hero described a mechanism that would secretly channel hot air from a fire on an altar and use it to open the temple doors. There was also an automatic theatre featuring thunder and fire, and a mirror that showed a goddess in place of the viewer’s reflection. Some scholars argue that Hero’s baroulkos – the geared machine for lifting heavy weights – was inspired as much by the trick of allowing a man to lift hundreds of times his weight as by the prospect of using it to do work.
Inspiring wonder in the masses by having metal animals come to life or temple doors mysteriously open played a role in keeping the lower classes in their place and stabilising the social order. Having knowledge and understanding of how the world worked was part of being in the Greek ruling elite. It also helped to impress the visiting Romans, who had an appetite for the Greeks’ scientific instruments as well as their art.
We know much less about the range of planetary mechanisms built than we do about Hero’s models, and if it wasn’t for the Antikythera fragments we wouldn’t be sure that they existed at all. But as well as fitting within a similar philosophical tradition, such devices may have been equally widespread.
The first argument for this relies on simple statistics. We have a very distorted view of ancient documents, because they only tended to survive if scribes throughout history thought they were worth copying. Unfortunately, this doesn’t mean that the best stuff survived – often quite the opposite. If intellectual standards dropped over time, for example, scribes didn’t copy the texts that represented the height of earlier scholarship because they couldn’t understand them; instead they ch
ose simpler works with popular appeal. Imagine some future civilisation judging our scientific knowledge based purely on hints from Friends and Big Brother.
With objects the situation is even worse, especially for anything made from valuable material like bronze, which, unless out of reach at the bottom of the sea, was inevitably melted down and recycled. Only a tiny fraction of what was made survives. For example, across the Greek world we know that there were hundreds of thousands – if not millions – of large bronze statues. Pliny wrote that there were 3,000 in the streets of Rhodes city alone, and this was in the first century AD, when the Roman-occupied island was a poor shadow of its former gleaming self. In the National Archaeological Museum in Athens, which has one of the best collections of Greek bronze statues in the world, there are now just ten. All but one are from shipwrecks.
So in terms of the Antikythera mechanism, the fact that we have found even one suggests that it can’t have been unique. We can’t say that such devices were ever mass produced, but there could have been dozens if not hundreds of them.
The sophistication of the mechanism supports this idea. This was not the work of a novice craftsman trying out his skills with clockwork for the first time. It would have taken practice, and once someone had the idea of using gearwheels to simulate the heavens, the design would probably have taken generations to perfect. The components of the mechanism are also very small – about as small as you could make them without needing eye glasses (which, as far as we know, the ancient Greeks didn’t have). The design and the maker’s skills must have been honed on a number of simpler, bigger mechanisms before being scaled down.
Finally, we have more clues from texts, which tell us that Posidonius wasn’t the only thinker linked to such a device. Cicero and several other Roman writers told of a similar instrument built by the great Archimedes, when he lived in Syracuse, Sicily, in the third century BC. Cicero described it as a sphere that showed the motions of the Sun, Moon and planets around the Earth. ‘The invention of Archimedes deserved special admiration because he had thought out a way to represent accurately by a single device for turning the globe those various and divergent movements with their different rates of speed,’ he wrote. ‘The Moon was always as many revolutions behind the Sun on the bronze contrivance as would agree with the number of days it was behind it in the sky.’
