The Antikythera Mechanism: A Computer from the Ancient World

A In the spring of 1901, a group of sponge divers sheltering from a fierce storm dropped anchor near the small Greek island of Antikythera, which lies between Crete and the mainland. Descending to the sea floor to pass the time, one of the divers surfaced in alarm, describing a heap of rotting corpses on the seabed below. What he had in fact stumbled upon was the wreck of an ancient ship, littered with corroded bronze and marble statues that had lain undisturbed for some two thousand years. Over the following months the divers recovered a remarkable haul of antiquities, and among the coins, jewellery and fine sculptures brought up from the deep was an unremarkable-looking lump of bronze, cracked and heavily encrusted, that at first attracted almost no attention at all.

B It was only later, in a museum in Athens, that the true importance of this shapeless object began to emerge. As the encrustation slowly dried and split apart, it revealed traces of finely cut gearwheels, their delicate teeth still visible in the green corroded metal. This was astonishing, for nothing of the kind was supposed to exist in the ancient world. Geared mechanisms of comparable precision were not thought to have been made until many centuries afterwards, and yet here was one apparently constructed by Greek craftsmen before the birth of Christ. The device, which came to be known as the Antikythera mechanism, was plainly no ordinary object, and it posed a question that would puzzle scholars for the best part of a century.

C For many decades the fragments resisted all attempts at understanding, since no one could open the fragile mass without destroying the very evidence they hoped to read. The breakthrough came at last from imaging techniques that could see inside the corroded metal without cutting it apart. Using powerful X-rays and, later, high-resolution three-dimensional scanning, researchers were able to count the teeth of gears buried deep within the object and to read faint inscriptions on its surfaces that the naked eye could never have detected. These hidden texts, a kind of instruction manual engraved on the device itself, turned out to be essential to working out exactly what the machine had been designed to do.

D The picture that gradually emerged was extraordinary. The mechanism was a hand-driven model of the heavens, a calculating machine that reproduced the movements of the sun and the moon as they appear from the Earth. By turning a small handle, a user could wind the device forwards or backwards in time and read off the position of the sun and moon against the constellations, together with the changing phase of the moon. It could indicate when eclipses were likely to occur, and it tracked several overlapping calendars, among them the cycle that governed the timing of the athletic games held across the Greek world. In effect, it packed a working knowledge of Greek astronomy into a wooden box small enough to be carried under one arm.

E What has most impressed modern scholars is the sheer sophistication of the design. The mechanism used dozens of interlocking bronze gears, including at least one ingenious arrangement that reproduced the irregular, speeding-and-slowing motion of the moon across the sky. Nothing of comparable complexity is known to survive from anywhere in the ancient world, and it would be well over a thousand years before clocks and astronomical instruments of similar intricacy appeared in medieval Europe. For a long time historians had assumed that the Greeks, for all their brilliance in geometry and philosophy, had never troubled to translate their theories into precision machinery. The Antikythera mechanism proved that comfortable assumption to be quite wrong.

F Many questions about the device remain unanswered even now. No one knows for certain who designed it, in which city it was made, or precisely why it was being carried aboard the ship when it sank. Some scholars have suggested that it was a teaching instrument, used to demonstrate the workings of the cosmos to students; others believe it was a treasured possession, displayed by a wealthy owner to advertise his learning. Nor is it clear whether the mechanism was a unique masterpiece or merely one of many such instruments, the rest of which have simply not survived the passage of time. What is certain is that it stands as a humbling reminder of how much ancient knowledge has been lost, and of how easily the finest achievements of the past can vanish almost without trace.