The AntiKythera Mechanism Revealed: A 2000-year old Astro-Computer

by Demetra George

Antikythera MechanismThe Antikythera Mechanism, a 2000-year old astronomical computer, is one of the most important current discoveries from the ancient world. It sheds light on a critical era of our own astrological history. This sophisticated multi-geared device, which is now dated to the late 3rd century BCE, is the world’s first known analog computer. Its purpose was to calculate and display precise positions of solar, lunar, stellar, and planetary phenomena. It was an eclipse predictor, an astrological tool for erecting charts, and an astronomical teaching device. Unlocking the mystery of this astronomical computer – how does it work, who built it, when, and for what purpose  – provides a glimpse into the misty origins of Hellenistic astrology.


Around 65 BCE, a ship set sail from Asia Minor, its cargo overloaded with looted Greek treasures from the Roman conquests of Eastern kingdoms. It carried coins from Pergamum and Ephesus and stopped at the islands of Kos and Rhodes to pick up vessels filled with oil and wine. As it rounded the tip southern Greece, it was caught up in a severe storm and sank near the tiny island of Antikythera. Its treasures remained buried beneath the sea, lost and undisturbed until 1900-01 when the cache was accidentally discovered by Greek sponge divers. Among the trove of glassware and marble and bronze statues were a number of pieces of a bronze geared mechanism, encrusted by two millennia of seashells and limestone accumulations. The fragments of the mechanism were placed in various boxes in the basement of the National Archaeological Museum of Athens and a few pieces eventually went on display with little explanatory commentary.

Over the next century, various museum curators, academics, historians, and researchers were intrigued with this mysterious device. Some even became obsessed for decades of their careers in an attempt to unravel its secrets. (1) In 1974, Derek de Solla Price described the antikythera mechanism as the cornerstone of computer’s technology and wrote that “it must surely rank as one of the greatest basic mechanical inventions of all time.” (2) A group of international scientists was formed in 2005 to further study the device’s significance and functions. (3) Using state-of-the-art x-ray and imaging techniques, the 82 fragments of the 32 known gears revealed evidence of the machine’s architectural engineering that incorporated the astronomical knowledge of its era, and even a user’s manual.

fragments of the Antikythera Mechanism

IMAGE: The surviving fragments of the Antikythera Mechanism. The 82 fragments that survive in the National Archaeological Museum in Athens are shown to scale.

The advanced technology of this machine would not be evident again in Western culture for another thousand years until the sophisticated clockwork of 14th century Europe. Instead, like many of the other Greek sciences, it would take an obscure and circuitous route through 6th century Byzantium, the Arabic world of the  11th century al-Biruni, and 13thcentury Moorish Spain before reappearing in the wave of translations from Arabic to Latin in 12th century Medieval Europe.

How Did it Work?

The antikythera mechanism was enclosed in wooden box about the size of a shoebox and driven by a handle on the side. On the front face was a fixed ring dial representing the ecliptic, marked off by equal 30-degree sectors bearing inscriptions of the Greek names of the twelve zodiacal signs. Outside that dial was a rotatable ring with the months of the Sothic calendar with the Egyptian names of the months transcribed into the letters of the Greek alphabet.

Turning a hand crank moved the date pointer on the front dial giving the position of the Sun which would then be set to the correct Egyptian calendar day. The action of turning the crank also caused all the other interlocked gears to rotate, calculating and displaying the positions of the Sun, Moon, moon phase, specific stars’ longitudes with their morning and evening risings, solar and lunar eclipses according to day of month, hour of day or night, direction, and color, and tentatively the locations of the planets and/or their first and last appearances and changes in direction. The device was calibrated to compensate for the extra quarter day in the solar year and the Moon’s faster and slower motions over the course of the month.

In order to determine precise eclipse times, the many gears include dials that tracked the Saros, Metonic, Exeligmos, and Callippic cycles according to the sidereal, synodic, and draconic months of the soli-lunar cycle. (4) The Olympiad dial gave a civil calendar for the year dates for the pan Hellenic games of Isthmia, Olympia, Nemea, Pythia, and the lesser games at Dodona and Rhodes, which were all used to keep political and religious chronologies. Astronomical calculations helped the Greeks to follow their traditions of sacrifices to the gods at the appropriate times of the year.

When, Where and Who Built It?

The answers to these questions are still shrouded in mystery with several different contenders vying for the credit of the invention, including several of the premiere geniuses of antiquity - Archimedes, Hipparchus and Poseidonius.

Hipparchus by RaphaelThe Case for Rhodes: An initial examination of the inscriptions dated them to around 150-100 BCE. Coupled with the evidence that the ship had stopped at the island of Rhodes, this suggested that the device might have been made there or at least was added to the cargo there. At that time, Rhodes was famed for its astronomical school, over which the great Greek astronomer Hipparchus presided from 140-120 BCE. Hipparchus employed geometry in the study of astronomical phenomena, invented trigonometry, predicted eclipses, and compiled the first star catalog by which he discovered the precession of the constellations. The initial reports in 2006 stated that the technology of the device mirrored his work. (5)

Another potential developer of this device considered by scholars is the Stoic philosopher Poseidonius (135-51 BCE) who succeeded Hipparchus as head of the school on Rhodes. The Roman orator Cicero, who studied under him, reported that Poseidonius had constructed a planetarium sphere that showed the movements of the sun, stars, and planets, by day and night, just as they appear in the sky. (6) Also in the running is the 1st century BCE astronomer Geminos, a student of Poseidonius, who included ideas in his Introduction to the Phenomena that resemble the inscriptions on the anikythera mechanism regarding the details of the names and numbers of the days of the months.

Rhodes is considered to be the potential place of invention or manufacture because it was a center of astronomy and engineering at that time; the calculations used in the prediction of eclipses on the antikythera mechanism were derived from the trigonometric methods developed by Hipparchus or his students. And the Olympiad dial on the antikythera mechanism included the name and dates for a minor athletic event that was held on Rhodes. (7)

ArchimedesThe Case for Syracuse or Corinth: In 2008, researchers discovered that the month names used in the Olympiad dials are from a local calendar used only in western Greece by colonies associated with Corinth, including Syracuse. (8) This pointed to the possible manufacture of the mechanism in the powerful city state of Syracuse, home to the most brilliant engineer and mathematical genius of the ancient world, Archimedes (287-212) who pioneered the use of gear wheels in his many inventions.

Archimedes, son of the astronomer Phidias, studied in Alexandria in his youth. He wrote a lost treatise on the construction of Sphere-Making and built a planetarium which showed the motions of the sun, moon, and five planets which was taken to Rome after his death. More than a century later, during the time of Cicero, Archimedes’ planetarium was described as an eclipse predictor:

“When Gallus moved the globe, it happened that the Moon followed the Sun by as many turns on that bronze contrivance as in the sky itself, from which also in the sky the Sun's globe became to have that same eclipse, and the Moon came then to that position which was its shadow on the Earth, when the Sun was in line.” (9)

The Syracuse/Corinth connection is based upon the local calendar names, astronomical calculations indicating observations that are thought to only be made in Corinth area. But perhaps the strongest case can be made because of the heritage of Archimedes’ unique genius in building geared mechanical devices that reflected his astronomical knowledge.

The Latest Findings

Jim EvansSeveral weeks ago, in November 2014, historian of astronomy Christian Carman and physicist James Evans published their latest findings after further analysis of the eclipse dial. (10) Their evidence suggests that the device works best if the full moon of month 1 of the Saros dial corresponds to May 12, 204 BCE, with the Exeligmos dial set at 0. Carmen and Evans pointed out the epoch date is not necessarily the same as the manufacture date, but that it would be surprising if they were widely separate.

Furthermore, they concluded that the Babylonian arithmetic scheme for predicting eclipse times matches the evidence better than does the trigonometric model. And finally that the longitudes for eclipses on the Saros dial encompassing the 18-year cycle from 204-186 BCE fit best for the Aegean Sea area.

While Evans remains cautious about attempting to identify the mechanism, his findings indicate that the device was likely built shortly after the death of Archimedes but almost a century before the flourishing of Hipparchus and his trigonometry methods for prediction of astronomical phenomena. He also points out that Rhodes is located in the Aegean Sea while Syracuse is not.

Alexander Jones, specialist in the history of ancient mathematical sciences at New York University places his bets on Rhodes as the site of manufacture. (11)

At this point in the inquiry as to origins, we can speculate that it was Archimedes’ advanced science, mechanics, engineering, and his astronomical planetarium prototype that provided the foundational models (and possibly even Corinthian month names for the Olympiad games dial) for the invention of the antikythera mechanism. In the late third century, when the device was built, Rhodes was a thriving intellectual center of technology and astronomy and it stood at the crossroads of trade and cultural exchange between Mesopotamia, Asia Minor, Greece and Rome. The time and place were conducive for some theorist in Rhodes to merge the arithmetic predictive methods of the Babylonians (which were accompanied by lists of actual observations with the models of Archimedes) in order to design the many interlocking gears of the mechanism. It could then have been built according to specifications by the local technicians.

Map of Hellenistic World

Implications for the History of Hellenistic Astrology

Historians of astrology have long been perplexed by the seemingly sudden emergence of a highly complex and sophisticated Hellenistic astrology over the course of a few generations. Its predecessor, Babylonian celestial divination had quite simpler interpretative texts, and at this time there is no evidence of any transitional texts documenting a gradual development of advanced techniques from Babylonian to Hellenistic astrologies. The antikythera mechanism may provide the missing key.

Babylonia had a long and rich history of celestial observations and corresponding omen divinations that were recorded on cuneiform clay tablets spanning the first two millennia BCE. Shortly before Alexander’s conquests of the lands of the ancient Near East in the late 4th century BCE, their astrology had culminated in the first horoscopes detailing the character and destiny of an individual based upon the planetary positions at the time of birth. Just a few simple interpretive texts have been discovered, which contain guidelines such as: “If a child is born when Jupiter comes forth and Mercury had set, it will go excellently for that man, his oldest son will die.” (12)

Babylonian astronomy included hundreds of ephemerides, almanacs, goal year texts and diaries that represented the systematic computation of daily planetary motions with risings, settings, visibility and direction changes, ingresses into different zodiacal signs, eclipses, and periodic planetary returns for predictive purposes.

Babylonian astronomical and astrological knowledge became available to the Greeks in the aftermath of Alexander’s conquests. Strabo tells us of Chaldean astrological schools at Babylon, Borsippa, Sippar and names of Chaldean astrologers Kidenas and Naburanos. (13) Berossus, a Babylonian priest, opened the first school of astrology in Greece in 290 BCE on the island Kos, adjacent to Rhodes. (14) Greek astrologers cited by ancient authors as having learned directly from Babylonian sources include: Sudines (fl. 250 BCE), astrological advisor to Attallus I in Pergamon; Apollonius of Myndos (fl. 225 BCE on the Carian coast of Asia Minor); and Epigenes of Byzantium and Critodemus. (15)

The Babylonian school for Greek astrologers on Kos was a short sail from Rhodes (the next island over) and Kos had strong political ties with the Ptolemaic kingdoms whose center was in Alexandria, Egypt. Within the next half century, the comprehensive astrological textbook of Nechepso and Petosiris appeared in Egypt circa 150 BCE. It contained significations of planets, four zodiacal rulership systems, elements, modalities, sect, houses, aspects, time lord systems, fixed stars, elaborate algorithms for determining length of life, critical periods, and analysis of the various topics of life such as marriage, children, wealth, rank, and health. This unique work established the foundation for the subsequent development of Hellenistic astrology and the Western tradition.

The invention and availability of a device such as the antikythera mechanism could have fostered this rapid advance of astrological practice. With a crank of the hand astrologers could compute planetary positions for charts much like we do today with the click of a finger on a mouse.

Jo Marchant points out that geared models that were similar to the antikythera mechanism were still being made in both Syracuse and Rhodes during the time of Cicero a century later. She speculates that Archimedes’ original design continued to be updated by the latest astronomical knowledge from Rhodes and elsewhere, and was shipped across the Greek-speaking world. (16)

In the 4th century CE, the Alexandrian mathematician Pappus includes in his discussion of the mechanical arts of his time that of sphere-makers who construct models of the heavens. (17) The antikythera mechanism is our first material evidence of this tradition that may have revolutionized the practice of astrology.

A colophon to this story emerged in my research for this essay: Robert Schmidt and others have struggled with the correct translation for the Greek word zoidion. While most astrologers refer to this word as a zodiacal sign and teach the zodiac as a circle of animals, the Greek lexicon entry includes “a small figure, painted or carved.” Schmidt settled upon “image” (of a small living creature) for his translation of zoidion.
It turns out that when Archimedes was in Alexandria, he was friends with the engineer Ctesbius, who specialized in modelling living creatures such as people, animals, and birds, as automated figures that were used on water clocks powered by steam, hot air, or water. This was a parallel tradition of Archimedes, who modelled planets in the heavens with geared devices. Small images of the zodiac animals might have been included upon the ecliptic ring of his planetariums.

Zoidion, one of the most important words for astrologers, can possibly be traced back to the youthful friendship of these two ancient sages, making moving models and images of the heavens and living creatures, one of whose later work would lead to the invention of the antikythera mechanism which in turn precipitated a quantum leap of astrology.

For the latest findings on the AntiKythera Mechanism, visit


(1) Naval historian Konstantinos Rados (1905), German philologist Albert Rehm (1907), Greek admiral J. Theophanides (1920’s), British physicist and historian of science Derek de Solla Price (from 1953 -1984), British museum curator of mechanical engineering Michael Wright (from 1983 to present)

(2) Derek de Solla Price, “Gears from the Greeks: “The Antikythera Mechanism – A Calendar Computer from ca. 80 BC,” in Transactions of the American Philosophical Society, 1974, 64.

(3) British professor of astronomy Mike Edmunds, British mathematician and film-maker Tony Freeth, Greek professors of astronomy J. Seiradakis and Xenophon Moussas. 

(4) The Saros Cycle is 223 synodic months equal to about 18 years; the Exeligmos cycle is 54-year triple Saros cycles; the Metonic cycle is 235 synodic months equal to about 19 tropical years; the Callippic cycle is 76 years equal to 4 Metonic cycles.

(5) Tony Freeth et al., “Supplementary Notes” in Calendars with Olympian display and eclipse prediction on the Antikythera Mechanism,” Nature 31, July 2008, 458, pp.614-17.

(6) Cicero, The Nature of the Gods 2.87-89.

(8) Tony Freeth, Alexander Jones, John M. Steele & Yanis Bitsakis  “Calendars with Olympic display and eclipse predictions on the Antikythera Mechanism” Nature 454, 614-617 (31 July 2008)

(9) Cicero The Rebublic 1.14

(10) Christian C. Carman and James Evans, “On the epoch of the Antikythera mechanism and its eclipse predictor,” in The Archive of History of Exact Sciences 68, Nov. 2014, pp.693-774.

(11)“On the Trail of an Ancient Mystery” in The New York Times, Nov. 24, 2014.

(12) From A. Sachs, “Babylonian Horoscopes,” in Journal of Cuneiform Studies 6 1952, 68-75.

(13) Strabo ,Geography 16.1–6.

(14) Vitruvius, On Architecture 9.6.2.

(15) Vettius Valens, The Anthology 9,11. Seneca, Natural Questions, 7.30. Neugebauer and Van Hoesen, Greek Horoscopes, Philadelphia: The American Philosophical Society Vol. 48, p. 185.

(16) Jo Marchant, Decoding the Heavens, Cambridge, MA: Da Capo Press, 2009, p. 288.

(17) Pappus of Alexandria, Mathematical Collection, Book 8.