The Antikythera mechanism is an ancient Greek device powered by hand, used to model the Solar System. It is the oldest known example of an analogue computer. This device could predict the positions of stars and planets, as well as eclipses, many years ahead. It could also track a four-year cycle of athletic competitions, similar to the ancient Olympic Games.

The artifact was discovered among wreckage from a shipwreck near the Greek island of Antikythera in 1901. In 1902, Greek politician Spyridon Stais noticed a gear inside the artifact during a visit to the National Archaeological Museum in Athens. His cousin, Valerios Stais, the museum director, began studying the fragment. The device was found as one piece, later split into three main parts. After conservation, these parts were divided into 82 smaller pieces. Four of these pieces contain gears, and many others have inscriptions. The largest gear was about 13 centimeters in diameter and originally had 223 teeth. All fragments are kept at the National Archaeological Museum, along with reconstructions and replicas, to show how the device may have looked and worked.

In 2005, a team from Cardiff University, led by Mike Edmunds, used advanced imaging techniques to study the mechanism’s inner parts and read faint inscriptions on its outer casing. These scans showed the device had 37 bronze gears that could track the Moon and Sun’s movement through the zodiac, predict eclipses, and model the Moon’s irregular orbit, where the Moon moves faster near Earth than when it is farther away. This motion was studied by astronomer Hipparchus of Rhodes in the 2nd century BC, and he may have influenced the device’s design. Some experts believe parts of the mechanism are missing and that it might have also calculated the positions of the five classical planets. In 2016, inscriptions were deciphered to reveal numbers related to the cycles of Venus and Saturn.

The instrument is believed to have been created by Hellenistic scientists. It has been dated to about 87 BC, between 150 and 100 BC, or 205 BC. It was made before the shipwreck, which is estimated to have occurred around 70–60 BC. In 2022, researchers suggested the mechanism’s initial calibration date might have been December 23, 178 BC. Other experts think 204 BC is a more likely calibration date. Machines of similar complexity did not appear again until the 14th century in western Europe.

History

In early 1900, Captain Dimitrios Kontos and a group of sponge divers from Symi island discovered the Antikythera wreck. During the first expedition with the Hellenic Royal Navy between 1900 and 1901, they recovered many items from the wreck. The wreck was a Roman cargo ship located 45 meters (148 feet) below the surface near Point Glyphadia on the Greek island of Antikythera. The team found bronze and marble statues, pottery, glassware, jewelry, coins, and the Antikythera mechanism. The mechanism was found in 1901, likely in July. It is unknown how the mechanism ended up on the ship.

All items from the wreck were sent to the National Museum of Archaeology in Athens for storage and study. At first, the mechanism looked like a lump of corroded bronze and wood. The bronze had changed into a material called atacamite, which cracked and shrank when removed from the wreck, altering the size of the pieces. Museum staff did not notice the mechanism for two years while focusing on other items, like statues. The mechanism was not treated after being removed from the water, causing further changes.

On May 17, 1902, archaeologist Valerios Stais and his cousin, Spyridon Stais, discovered a piece of rock with a gear wheel inside. Stais first thought it was an astronomical clock, but many scholars believed the device was too advanced for its time. Albert Rehm, a German philologist, was the first to suggest it might be an astronomical calculator.

Research on the object stopped until 1951, when British science historian Derek J. de Solla Price became interested. In 1971, Price and Greek physicist Charalampos Karakalos used X-ray and gamma-ray images to study the 82 fragments of the mechanism. Price published his findings in 1974.

In 2012 and 2015, two more searches at the wreck site found art objects and a second ship, possibly connected to the original ship that carried the mechanism. A bronze disc with a bull image and four holes was also found. It was thought to be part of the mechanism but is more likely a decorative object.

The Antikythera mechanism is considered the first known analogue computer. Its complexity suggests it had earlier predecessors during the Hellenistic period. It used theories of astronomy and mathematics developed by Greek astronomers around the second century BC. It is estimated to have been built in the late second century BC or early first century BC.

In 2008, research suggested the mechanism’s concept may have originated in Corinth’s colonies, as the calendar on the Metonic Spiral matched Corinthian styles. Syracuse, a Corinthian colony and home to Archimedes, was considered a possible connection. However, later studies showed the calendar was Corinthian, not Syracusan. Another theory links the mechanism to Pergamon, based on coins found by Jacques Cousteau in the 1970s. Pergamon was home to the Library of Pergamum, a major center of learning.

The wreck contained Rhodian-style vases, leading to the idea that the mechanism was made at an academy on Rhodes, a hub for astronomy and engineering. Rhodes was home to Hipparchus, who developed theories about the Moon’s motion used in the mechanism. Studies suggest the mechanism’s predictions match latitudes near Rhodes.

In 2014, a study proposed the mechanism was made around 200 BC, based on the Saros Dial’s start date. Another study in 2017 argued the prototype was from Rhodes but modified for a client in Epirus, likely built no earlier than a generation before the wreck.

Further dives in 2014 and 2015 aimed to find more of the mechanism. A five-year research program ran from 2014 to 2019, with another session starting in 2020.

In 2022, researchers suggested the mechanism’s calibration date might be 23 December 178 BC, though others believe 204 BC is more likely. Similar devices did not reappear until the 14th century, with examples like the astronomical clocks of Richard of Wallingford and Giovanni de’ Dondi.

Design

The original mechanism was found as a single piece covered in deposits from the Mediterranean Sea. It then broke into three large pieces. Over time, more small pieces broke off during cleaning and handling. The Cousteau expedition later found some fragments on the sea floor. Other fragments may still be stored and not yet discovered, like Fragment F, which was found in 2005. Of the 82 known fragments, seven are important for understanding how the mechanism works and contain most of its parts and writings. Another 16 smaller parts have partial or incomplete writings.

Fragment A includes parts of the upper left section of the Saros spiral and 14 writings from that spiral. It also contains writings related to the exeligmos dial. On the back of the fragment, parts of the dial face remain visible. Additionally, this fragment includes some back door writings.

Many of the smaller fragments found so far do not have valuable information, but a few have writings. Fragment 19 has important back door writings, including one that says "… 76 years …" and refers to the Callippic cycle. Other writings seem to explain the purpose of the back dials. In addition to Fragment 19, 15 other small fragments have traces of writings on them.

Mechanics

Information about the specific data from the fragments is explained in the supplement to the 2006 Nature article by Freeth et al.

On the front of the mechanism, there is a fixed ring dial that shows the ecliptic, divided into 12 equal 30-degree sections for the zodiac signs. This matches the Babylonian practice of dividing the ecliptic equally among the zodiac signs, even though the actual boundaries of the constellations varied. Around this dial is another ring that can be turned. It is marked with the months and days of the Sothic Egyptian calendar, which includes 12 months of 30 days each, plus five extra days. The months are labeled with Egyptian names written in the Greek alphabet. To use the mechanism, the Egyptian calendar ring must first be rotated to align with the current zodiac positions. The Egyptian calendar did not account for leap days, so it shifted by one zodiac sign every 120 years.

The mechanism was operated by turning a small hand crank (now lost), which connected to a large gear on the front of fragment A, gear b1. This gear moved a date pointer on the front dial, which was set to the correct Egyptian calendar day. The year could not be selected, so the user had to know the current year or refer to the Babylonian ephemeris tables on the back of the mechanism to find the correct information for the selected day. The crank moved the date pointer about 78 days per full rotation, making it easy to reach a specific day if the mechanism was working properly. Turning the crank also caused all connected gears to move, allowing the mechanism to calculate the positions of the Sun and Moon, the moon phase, eclipses, calendar cycles, and possibly the locations of planets.

The operator also had to pay attention to spiral dial pointers on two large dials on the back. These pointers had a "follower" that followed spiral grooves in the metal as the dials made four or five full rotations. When a pointer reached the end of the spiral, the follower had to be moved manually to the other end before continuing.

The front dial has two circular scales. The inner scale marks the Greek zodiac signs with degree divisions. The outer scale is a movable ring that fits into a channel and is marked with what appear to be days, with holes beneath the ring in the channel.

Since the mechanism was discovered over 100 years ago, the outer ring was thought to represent a 365-day Egyptian solar calendar. However, research by Budiselic et al. (2020) found 354 intervals, suggesting it might instead represent a lunar calendar. Two research teams independently confirmed this, with Woan and Bayley finding 354–355 intervals and Malin and Dickens estimating 352.3±1.5. These results suggest the number of holes (N) is most likely between 350 and 355, with a very low chance of being 365.

If the 365-day calendar is accepted, the mechanism predates the Julian calendar reform but reflects earlier knowledge of a 365 + 1/4-day solar year, as seen in Ptolemy III’s attempted calendar reform in 238 BC. The outer dial may have been adjusted to account for the extra quarter-day by moving backward one day every four years.

If the 354-day evidence is correct, the ring likely represents a lunar calendar. This would align with the Egyptian month names on the dial and could be the first example of the Egyptian civil-based lunar calendar proposed by Richard Anthony Parker in 1950. The lunar calendar would have helped track lunar phases and assist with interpreting the Metonic and Saros dials. Unseen gears, connected to the Metonic system, may have driven a pointer around the scale. Adjusting the ring relative to the holes would have allowed corrections for the Callippic cycle and lunisolar intercalation.

The dial also shows the Sun’s position on the ecliptic, matching the current date. The orbits of the Moon and the five known Greek planets are close to the ecliptic, making it a useful reference for their positions.

The following three Egyptian months are written in Greek letters on the surviving parts of the outer ring:
– [Month names omitted for brevity]

Other months have been reconstructed, though some reconstructions exclude the five intercalary days of the Egyptian calendar. The zodiac dial includes Greek inscriptions for the zodiac signs, likely adapted to the tropical month version rather than the sidereal.

On the zodiac dial, single characters mark specific points, corresponding to a parapegma—an early form of an almanac—inscribed on the front face above and below the dials. These characters indicate the longitudes of specific stars on the ecliptic. The parapegma above the dials reads:
– [Text omitted for brevity]

The parapegma below the dials reads:
– [Text omitted for brevity]

At least two pointers showed positions of celestial bodies on the ecliptic. A lunar pointer showed the Moon’s position, and a mean Sun pointer likely also indicated the current date. The Moon’s position was not a simple average but approximated its elliptical orbit’s acceleration and deceleration using epicyclic gearing. The mechanism also tracked the Moon’s orbit’s precession over an 8.88-year cycle. The mean Sun’s position equals the current date. While a "true sun" pointer may have existed to track Earth’s elliptical orbit around the Sun, no evidence of it was found. Similarly, no evidence of planetary orbit pointers for the five known Greek planets was found.

Mechanical engineer Michael Wright showed the mechanism included a lunar phase indicator. A small ball, half-white and half-black, was embedded in the lunar pointer and rotated to show the phase (new, first quarter, half, third quarter, full, and back). This function is supported by the Sun and Moon’s angular positions, which determine the angle between them.

Reconstruction efforts

The large space between the mean Sun gear and the front of the case, along with the size and features of the mean Sun gear, suggests that the device likely had more gears. These gears may have been lost during or after the shipwreck or removed before the device was placed on the ship. Because there is little evidence about the front part of the device, many people have tried to guess what the Ancient Greeks might have built. Over time, new discoveries have helped scientists rule out old ideas and create better models.

In the 1970s, Derek J. de Solla Price built a simple model of the device.

In 2002, Michael Wright created the first working model using what was known about the device. He believed the device could show the movement of the Sun and planets, including adjustments for the Sun’s irregular motion (called the "first anomaly"). His model included pointers for the "true sun," Mercury, Venus, Mars, Jupiter, and Saturn, in addition to the "mean sun" and lunar pointers.

In 2010, Evans, Carman, and Thorndike proposed a different model. They noticed that the inscriptions on the front dial were unevenly spaced, which they thought meant the Sun’s pointer was not centered. This idea simplified the device by removing the need to track the Sun’s irregular motion. Instead, they suggested simple dials for each planet, showing events like when planets appeared in the sky or changed direction. This system used fewer gears and was easier to build than Wright’s model.

Their model used simple gears and explained the purpose of a 63-toothed gear found in a fragment of the device. They proposed two designs for the front dial and used weather and seasonal icons displayed through a window instead of gears and axles. In 2012, they also suggested a system of gears with pins and slots.

In 2012, Freeth and Jones proposed a compact model for showing planetary motion. They suggested using a separate pointer for the Sun’s irregular motion, different from the pointer showing the average Sun position and date. If the two dials are aligned correctly, their model’s front display looks similar to Wright’s. However, this model has not been built physically and only exists as a computer simulation.

The system for showing the Sun’s irregular motion is similar to Wright’s: three gears, one fixed in the center of the b1 gear and attached to the Sun’s spindle, a second gear acting as a helper, and a third gear with an offset pin. This pin moves a slot on an arm connected to the Sun’s spindle, creating the irregular motion.

The mechanism for tracking the Sun, Mercury, and Venus uses epicyclic gears (a type of gear system that moves in circles). Each planet’s gear is attached to the b1 gear and connects to a fixed gear in the device. A pin on each gear moves a bar with a slot, which controls a pointer for the planet. These bars avoid interference between the three systems and use only five gears and three slotted bars.

For Mars, Jupiter, and Saturn, the system works like the one for the Moon’s irregular motion. Each planet’s gear is attached to an extension of the b1 gear and connects to a fixed gear. A pin on each gear moves a bar with a slot, which controls a pointer for the planet. All three systems fit into one section of the device and use 12 additional gears.

In total, the device has eight spindles of different sizes to move eight pointers. This includes 30 original gears, seven added for the calendar, and 17 gears and three slotted bars for the six new pointers. Freeth and Jones’ model uses 54 gears, three bars, and eight pointers.

On a visual drawing, the pointers on the front zodiac dial have small, round stones to identify them. This idea comes from an ancient papyrus that describes using stones for the Sun, Moon, and planets.

Recent discoveries have shown that earlier models were not accurate. In 2016, scientists found the numbers 462 and 442 in scans of the device. These numbers relate to how often Venus and Saturn return to the same position in the sky, showing the device was more precise than previously thought. In 2018, researchers used these findings to create new mechanical parts for the device.

In 2021, a team at University College London, led by Freeth, proposed a new reconstruction of the entire device. They found that some gears could be shared among different planetary systems by using simple math. Their model matches all known data, unlike earlier models. Freeth explained these discoveries in a video.

In 2025, further research may continue to improve understanding of the device.

Similar devices in ancient literature

The level of detail in the mechanism shows that the device was not unique and likely required knowledge passed down through many generations. However, such objects were often melted down for their bronze value and rarely survived until today.

Cicero’s De re publica (written between 54–51 BC), a philosophical discussion from the first century BC, describes two machines that some modern writers believe were similar to a planetarium or orrery, used to predict the movements of the Sun, Moon, and the five known planets of that time. Both were created by Archimedes and taken to Rome by the Roman general Marcus Claudius Marcellus after Archimedes died during the siege of Syracuse in 212 BC. Marcellus respected Archimedes greatly, and one of these machines was the only item he kept from the siege (the other was placed in the Temple of Virtue). The device was passed down as a family treasure. Cicero wrote that in a conversation imagined to have taken place in the villa of Scipio Aemilianus in 129 BC, a character named Philus said that Gaius Sulpicius Gallus (a Roman official and writer on eclipses) explained and demonstrated the device’s function.

I had often heard of this celestial globe because of Archimedes’ fame, but its appearance did not seem especially impressive. Another, more elegant model, also made by Archimedes and placed in the Temple of Virtue by Marcellus, was more widely known. When Gallus explained the device’s design, I realized Archimedes must have had a mind far greater than most people imagined. Gallus said the solid globe was an ancient invention, first created by Thales of Miletus. Later, Eudoxus of Cnidus, a student of Plato, added stars to its surface. Aratus later described these stars in poetry, not through scientific study. Gallus explained that the original solid globe could not show the motions of the Sun, Moon, and five planets, but Archimedes’ invention could. His design allowed a single rotation to represent different movements of these celestial bodies. When Gallus moved the globe, it showed the Moon’s relationship with the Sun, and the number of turns on the bronze device matched the number of days in the real sky. This demonstrated both solar and lunar eclipses.

Pappus of Alexandria (290–c. 350 AD) wrote that Archimedes had composed a now-lost manuscript titled On Sphere-Making, which described these devices. Ancient texts mention many of Archimedes’ inventions, some with simple drawings. One example is his odometer, a device later used by the Romans to mark mile distances (described by Vitruvius, Heron of Alexandria, and during Emperor Commodus’ time). The drawings in the text looked functional, but attempts to build them as shown failed. However, replacing square-toothed gears with angled gears like those in the Antikythera mechanism made the device work.

If Cicero’s account is accurate, this technology existed as early as the third century BC. Later Roman writers, such as Lactantius, Claudian, and Proclus, also mentioned Archimedes’ device in the fourth and fifth centuries. Cicero also noted that his friend Posidonius built a similar device “recently,” which replicated the daily movements of the Sun, Moon, and five planets.

It is unlikely that any of these machines was the Antikythera mechanism found in the shipwreck, as the devices described by Cicero were in Rome at least 30 years after the shipwreck’s estimated date. The third device was likely in Posidonius’ possession by then. Scientists who studied the Antikythera mechanism agree it was too advanced to be a one-of-a-kind creation.

Other complex metal devices from Roman Greece include a bronze combination lock from the Augustan or Hadrianic period, found in Kerameikos. This lock used a simple mechanical system: a central bolt could not be moved until two rotating dials were correctly aligned. It also had a hidden bypass mechanism.

Evidence that the Antikythera mechanism was not unique supports the idea that ancient Greeks developed advanced mechanical technology, which later influenced the Byzantine and Islamic worlds. In the Byzantine Empire, a fifth- or sixth-century sundial with a geared calendar was found, possibly used to tell time. In the Islamic world, the Kitab al-Hiyal (Book of Ingenious Devices), written in the early 9th century, described over 100 mechanical devices, some based on ancient Greek texts. A similar geared calendar was described by al-Biruni around 1000 AD, and a 13th-century astrolabe included a comparable clockwork device. These technologies may have reached Europe and helped develop mechanical clocks.

In the 11th century, the Chinese scholar Su Song built a mechanical clock tower that tracked the positions of stars and planets, displayed on a rotating armillary sphere.

Popular culture and museum replicas

Many exhibitions have been held around the world, with the main "Antikythera shipwreck" exhibition taking place at the National Archaeological Museum in Athens. As of 2012, the Antikythera mechanism was shown in a temporary exhibition about the shipwreck, along with models created by Ioannis Theofanidis, Derek de Solla Price, Michael Wright, Thessaloniki University, and Dionysios Kriaris. Other models are displayed at the American Computer Museum in Bozeman, Montana; the Children's Museum of Manhattan in New York; the Astronomisch-Physikalisches Kabinett in Kassel, Germany; the Archimedes Museum in Olympia, Greece; the Kotsanas Museum of Ancient Greek Technology in Athens; the Musée des Arts et Métiers in Paris; and the Western Australian Museum.

The National Geographic TV show Naked Science had an episode about the Antikythera Mechanism titled "Star Clock BC," which aired on January 20, 2011. A film called The World's First Computer was made in 2012 by researcher and filmmaker Tony Freeth. In 2012, BBC Four broadcast The Two-Thousand-Year-Old Computer. It was also shown on April 3, 2013, in the United States on NOVA, a PBS science program, under the name Ancient Computer. The film describes the discovery and 2005 study of the mechanism by the Antikythera Mechanism Research Project.

In 2010, a working model of the Antikythera mechanism was built using Lego bricks by a hobbyist named Andy Carol. It was shown in a short film made by Small Mammal in 2011.

On May 17, 2017, Google honored the 115th anniversary of the mechanism's discovery with a special Google Doodle.

The YouTube channel Clickspring shows the making of a replica of the Antikythera mechanism using tools, methods, and materials that were likely available in ancient Greece. It also explores possible technologies from that time.

The movie Indiana Jones and the Dial of Destiny (2023) includes a fictional version of the mechanism, called the "Archimedes' Dial" or "Dial of Destiny." In the film, the device was created by Archimedes as a tool to track time and was sought by a former Nazi scientist to find time portals and help Germany win World War II. A key part of the story is that the device did not consider continental drift, a theory that was unknown in Archimedes' time.

On February 8, 2024, a 10X scale replica of the mechanism was built, placed, and officially opened at the University of Sonora in Hermosillo, Sonora, Mexico. Named the Monumental Antikythera Mechanism for Hermosillo (MAMH), Dr. Alfonso performed the opening ceremony. Also present were Durazo Montaño, the Governor of Sonora; Dr. Maria Rita Plancarte Martinez, the chancellor of the Universidad de Sonora; the ambassador of Greece, Nikolaos Koutrokois; and a group from the Greek Embassy.

In 2024, the Finnish band Nightwish included a song called "Antikythera Mechanism" on their album Yesterwynde. The band also worked with a Finnish watchmaker, POOK Watches, to create a special edition watch that includes design elements inspired by the Antikythera Mechanism.