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The GPS of the Romans? The Antikythera mechanism

Working out where you are is fundamental to all navigation. Today, we largely depend on GPS satellites to do the job for us. But the people of ancient Greece and Rome didn’t have that option, of course. So they used the next best thing – stars.

antikythera

But the secrets of how they did it are still shrouded in some mystery. Map historian CJ Schuler – who previously covered the ‘digital maps of the Romans’ for this site – describes the path to unlocking an ancient device that is one of the forefathers of today’s mobile mapping.

 

In October 1900, a Greek ship returning from a sponge-fishing expedition off the North African coast ran into a storm north of Crete. Taking shelter alongside the small island of Antikythera (also known as Tsirigoto), whose tiny population was mostly engaged in fishing, beekeeping and vine-growing, the captain sent down a diver to see if he could harvest any more sponges. 

Amid such glamorous finds, one heavily oxidized lump of material sat unnoticed in a storeroom for two years until some of the encrustation fell away and the archaeologist Valerios Stais noticed that it contained a series of metal gearwheels. Since then, it has taken more than a century of advancing technology to coax out the secrets of this enigmatic device.

100 years later

DerekdeSollaPrice_smIn 1974, the British science historian Derek de Solla Price used gamma radiography to reveal much of the internal mechanism, including a differential gear, a device previously considered to have been unknown in the ancient world. The largest fragment contained 27 hand-cut bronze cogwheels. While parts were missing, enough survived to establish that the machine, driven by a hand crank on the side, was intended to show the movements of the Moon, Sun, and the five planets known to the ancients. The complete mechanism would have been just over 12 inches high, and was housed in a rectangular wooden frame with two doors, each of which had a bronze plate inscribed with instructions.

In 1976, a second dive by JY Cousteau’s oceanographic survey vessel Calypso recovered several smaller fragments, along with coins from the Greek cities on the coast of Asia Minor, which suggested that the ship had sailed from there around 70–60 BC, carrying booty back to Rome.

 

In the 1990s, Michael Wright, curator of Mechanical Engineering at the Science Museum in London, made a completely new study of the original fragments using linear X-ray tomography, a technique similar to hospital CAT scans. It increased Price’s gear count of 27 to 31, identified an ingenious train of gears to display the phases of the Moon, and revealed further inscriptions that dated the device to around 150–100 BC. They included a manual with astronomical, mechanical and geographical sections. Further studies published in 2008 demonstrated that the mechanism also contained a dial to show which of the ancient Greek games – including the Olympics – were due to take place in any year.

 

 

Although nothing like the Antikythera mechanism has been found, it cannot have been unique in the ancient world; a device of such sophistication could only have been produced by experienced engineers working in a well-established tradition. The literary evidence supports this. In his book De Re Publica – written about a decade after the Antikythera ship went down – Cicero mentions that Archimedes had built a machine composed of spheres that displayed the motions of the Sun and Moon, the planets, and solar and lunar eclipses. He also mentions another such device built by his friend Posidonius of Rhodes (c. 135–51 BC), “each one of the revolutions of which brings about the same movement in the Sun and Moon and five wandering stars [planets] as is brought about each day and night in the heavens.”

Mysteries remain

Although the Antikythera device is portable, and the instructions suggest that it was designed to be used by someone other than its maker, it was probably not intended for shipboard navigation; it was too delicate, too complex, and too rare. Some of the data it could generate, such as eclipse predictions, had no direct navigational application, and salt spray would quickly corrode the gears. The machine’s computing power, however, would have enabled its user to generate astronomical tables with which navigators could calculate their position.

An exploratory expedition, led by Brendan Foley and armed with the latest diving equipment, revisited the wreck in 2012, recovering the ship’s anchor and preparing for a major investigation to be launched this year. It will be fascinating to see what else it may reveal about the world’s earliest known geographical and astronomical computer.

 

 

image credits: Wikimedia

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