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Discovering How Greeks Computed in 100 B.C.


Published: July 31, 2008

After a closer examination of a surviving marvel of ancient Greek technology known as the Antikythera Mechanism, scientists have found that the device not only predicted solar eclipses but also organized the calendar in the four-year cycles of the Olympiad, forerunner of the modern Olympic Games.

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The new findings, reported Wednesday in the journal Nature, also suggested that the mechanism’s concept originated in the colonies of Corinth, possibly Syracuse, on Sicily. The scientists said this implied a likely connection with Archimedes.

Archimedes, who lived in Syracuse and died in 212 B.C., invented a planetarium calculating motions of the Moon and the known planets and wrote a lost manuscript on astronomical mechanisms. Some evidence had previously linked the complex device of gears and dials to the island of Rhodes and the astronomer Hipparchos, who had made a study of irregularities in the Moon’s orbital course.

The Antikythera Mechanism, sometimes called the first analog computer, was recovered more than a century ago in the wreckage of a ship that sank off the tiny island of Antikythera, north of Crete. Earlier research showed that the device was probably built between 140 and 100 B.C.

Only now, applying high-resolution imaging systems and three-dimensional X-ray tomography, have experts been able to decipher inscriptions and reconstruct functions of the bronze gears on the mechanism. The latest research has revealed details of dials on the instrument’s back side, including the names of all 12 months of an ancient calendar.

In the journal report, the team led by the mathematician and filmmaker Tony Freeth of the Antikythera Mechanism Research Project, in Cardiff, Wales, said the month names “are unexpectedly of Corinthian origin,” which suggested “a heritage going back to Archimedes.”

No month names on what is called the Metonic calendar were previously known, the researchers noted. Such a calendar, as well as other knowledge displayed on the mechanism, illustrated the influence of Babylonian astronomy on the Greeks. The calendar was used by Babylonians from at least the early fifth century B.C.

Dr. Freeth, who is also associated with Images First Ltd., in London, explained in an e-mail message that the Metonic calendar was designed to reconcile the lengths of the lunar month with the solar year. Twelve lunar months are about 11 days short of a year, but 235 lunar months fit well into 19 years.

“From this it is possible to construct an artificial mathematical calendar that keeps in synchronization with both the sun and the moon,” Dr. Freeth said.

The mechanism’s connection with the Corinthians was unexpected, the researchers said, because other cargo in the shipwreck appeared to be from the eastern Mediterranean, places like Kos, Rhodes and Pergamon. The months inscribed on the instrument, they wrote, are “practically a complete match” with those on calendars from Illyria and Epirus in northwestern Greece and with the island of Corfu. Seven months suggest a possible link with Syracuse.

Inscriptions also showed that one of the instrument’s dials was used to record the timing of the pan-Hellenic games, a four-year cycle that was “a common framework for chronology” by the Greeks, the researchers said.

“The mechanism still contains many mysteries,” Dr. Freeth said. Among the larger questions, scientists and historians said the place of the mechanism in the development of Greek technology remained poorly understood. Several references to similar instruments appear in classical literature, including Cicero’s description of one made by Archimedes. But this one, hauled out of the sea in 1901, is the sole surviving example.


Early Astronomical ‘Computer’ Found to Be Technically Complex


Published: November 30, 2006

A computer in antiquity would seem to be an anachronism, like Athena ordering takeout on her cellphone.

Decoding the Ancient Greek Astronomical Calculator Known as the Antikythera Mechanism (Nature)

But a century ago, pieces of a strange mechanism with bronze gears and dials were recovered from an ancient shipwreck off the coast of Greece. Historians of science concluded that this was an instrument that calculated and illustrated astronomical information, particularly phases of the Moon and planetary motions, in the second century B.C.

The instrument, the Antikythera Mechanism, sometimes called the world’s first computer, has now been examined with the latest in high-resolution imaging systems and three-dimensional X-ray tomography. A team of British, Greek and American researchers deciphered inscriptions and reconstructed the gear functions, revealing “an unexpected degree of technical sophistication for the period,” it said.

The researchers, led by the mathematician and filmmaker Tony Freeth and the astronomer Mike G. Edmunds, both of the University of Cardiff, Wales, are reporting their results today in the journal Nature.

They said their findings showed that the inscriptions related to lunar-solar motions, and the gears were a representation of the irregularities of the Moon’s orbital course, as theorized by the astronomer Hipparchos. They established the date of the mechanism at 150-100 B.C.

The Roman ship carrying the artifacts sank off the island of Antikythera about 65 B.C. Some evidence suggests it had sailed from Rhodes. The researchers said that Hipparchos, who lived on Rhodes, might have had a hand in designing the device.

In another Nature article, a scholar not involved in the research, François Charette of the University of Munich museum, in Germany, said the new interpretation of the mechanism “is highly seductive and convincing in all of its details.” It is not the last word, he said, “but it does provide a new standard, and a wealth of fresh data, for future research.”

Technology historians say the instrument is technically more complex than any known for at least a millennium afterward. Earlier examinations of the instrument, mainly in the 1970s by Derek J. de Solla Price, a Yale historian who died in 1983, led to similar findings, but they were generally disputed or ignored.

The hand-operated mechanism, presumably used in preparing calendars for planting and harvesting and fixing religious festivals, had at least 30, possibly 37, hand-cut bronze gear-wheels, the researchers said. A pin-and-slot device connecting two gear-wheels induced variations in the representation of lunar motions according to the Hipparchos model of the Moon’s elliptical orbit around Earth.

The numbers of teeth in the gears dictated the functions of the mechanism. The 53-tooth count of certain gears, the team said, was “powerful confirmation of our proposed model of Hipparchos’ lunar theory.” The detailed imaging revealed more than twice the inscriptions recognized earlier. Some of these appeared to relate to planetary and lunar motions. Perhaps, the team said, the mechanism also had gearings to predict the positions of known planets.

Dr. Charette noted that more than 1,000 years elapsed before instruments of such complexity are known to have re-emerged. A few artifacts and some Arabic texts suggest that simpler geared calendrical devices had existed, particularly in Baghdad around A.D. 900.

It seems clear, he said, that “much of the mind-boggling technological sophistication available in some parts of the Hellenistic and Greco-Roman world was simply not transmitted further.”

“The gear-wheel, in this case,” he added, “had to be reinvented.”



Nature 444, 587-591 (30 November 2006) | doi:10.1038/nature05357; Received 10 August 2006; Accepted 17 October 2006

Decoding the ancient Greek astronomical calculator known as the Antikythera Mechanism

T. Freeth1,2, Y. Bitsakis3,5, X. Moussas3, J. H. Seiradakis4, A. Tselikas5, H. Mangou6, M. Zafeiropoulou6, R. Hadland7, D. Bate7, A. Ramsey7, M. Allen7, A. Crawley7, P. Hockley7, T. Malzbender8, D. Gelb8, W. Ambrisco9 and M. G. Edmunds1

  1. Cardiff University, School of Physics and Astronomy, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
  2. Images First Ltd, 10 Hereford Road, South Ealing, London W5 4SE, UK
  3. National and Kapodistrian University of Athens, Department of Astrophysics, Astronomy and Mechanics, Panepistimiopolis, GR-15783, Zographos, Greece
  4. Aristotle University of Thessaloniki, Department of Physics, Section of Astrophysics, Astronomy and Mechanics, GR-54124 Thessaloniki, Greece
  5. Centre for History and Palaeography, National Bank of Greece Cultural Foundation, P. Skouze 3, GR-10560 Athens, Greece
  6. National Archaeological Museum of Athens, 1 Tositsa Str., GR-10682 Athens, Greece
  7. X-Tek Systems Ltd, Tring Business Centre, Icknield Way, Tring, Hertfordshire HP23 4JX, UK
  8. Hewlett-Packard Laboratories, 1501 Page Mill Road, Palo Alto, California 94304, USA
  9. Foxhollow Technologies Inc., 740 Bay Road, Redwood City, California 94063, USA

Correspondence to: M. G. Edmunds1 Correspondence and requests for materials should be addressed to M.G.E. (Email:


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The Antikythera Mechanism is a unique Greek geared device, constructed around the end of the second century bc. It is known1, 2, 3, 4, 5, 6, 7, 8, 9 that it calculated and displayed celestial information, particularly cycles such as the phases of the moon and a luni-solar calendar. Calendars were important to ancient societies10 for timing agricultural activity and fixing religious festivals. Eclipses and planetary motions were often interpreted as omens, while the calm regularity of the astronomical cycles must have been philosophically attractive in an uncertain and violent world. Named after its place of discovery in 1901 in a Roman shipwreck, the Antikythera Mechanism is technically more complex than any known device for at least a millennium afterwards. Its specific functions have remained controversial11, 12, 13, 14 because its gears and the inscriptions upon its faces are only fragmentary. Here we report surface imaging and high-resolution X-ray tomography of the surviving fragments, enabling us to reconstruct the gear function and double the number of deciphered inscriptions. The mechanism predicted lunar and solar eclipses on the basis of Babylonian arithmetic-progression cycles. The inscriptions support suggestions of mechanical display of planetary positions9, 14, 15, now lost. In the second century bc, Hipparchos developed a theory to explain the irregularities of the Moon's motion across the sky caused by its elliptic orbit. We find a mechanical realization of this theory in the gearing of the mechanism, revealing an unexpected degree of technical sophistication for the period.