The Antikythera Mechanism: What Its Hidden Inscriptions Reveal

The Antikythera Mechanism: Reading the Evidence in Its Gears

The Antikythera Mechanism is a hand-cranked bronze device built by Greek craftsmen more than 2,000 years ago to model the sky. Turn its handle and its gears moved pointers that showed the positions of the Sun and Moon against the zodiac, the phases of the Moon, the dates of coming eclipses and the four-year cycle of the great athletic games. It is often called the world’s first known analogue computer, and nothing of comparable mechanical complexity is known again until the astronomical clocks of 14th-century Europe.

In June 2016, after more than a decade of work, an international research team announced that it had read thousands of tiny letters hidden on the corroded fragments. Those texts, effectively a description of the dials engraved on the machine itself, settled several long-running questions and raised a few surprising new ones. Here is what the mechanism is, how researchers read it, and what the inscriptions really tell us.

Found in a shipwreck by sponge divers

In 1900 sponge divers from the island of Symi discovered an ancient wreck about 45 metres down off the small island of Antikythera, between Kythera and Crete. Over the following year, in one of the first major underwater archaeological recoveries, they brought up bronze and marble statues, glassware, pottery and coins. The ship had sunk around 70–60 BCE, probably carrying luxury goods westward towards Italy.

Among the finds was an unremarkable lump of corroded bronze and wood. In May 1902, at the National Archaeological Museum in Athens, the archaeologist Valerios Stais and his cousin Spyridon noticed a gear wheel embedded in it. Since then the lump has separated into three main pieces and dozens of smaller ones, today counted as 82 fragments. Four of them contain gears; the largest wheel is about 13 centimetres across and once had 223 teeth.

The fragments are still displayed in Athens, together with modern reconstructions and replicas.

A close-up of the mechanism’s fragments on display at the National Archaeological Museum in Athens. Photo: Garrett Ziegler/Flickr (CC BY-NC-ND 2.0).

What the mechanism did

The device was originally housed in a wooden case roughly the size of a shoebox, with dials on the front and back. Scans suggest it contained around 35 meshing bronze gears, of which about 30 survive. From what remains, researchers have identified these functions:

Front dial: the positions of the Sun and Moon in the zodiac and against a calendar, plus a small rotating ball that showed the Moon’s phase.
Metonic dial: a spiral tracking the 235-month cycle that brings lunar months and solar years back into step after 19 years.
Saros dial: a spiral covering 223 lunar months, about 18 years, the classic cycle used to predict eclipses. A smaller exeligmos dial, three Saros cycles long, corrected the predicted times.
Callippic dial: a 76-year refinement of the Metonic cycle.
Games dial: the four-year cycle of the Panhellenic games, including the Olympics.

Whether the original also displayed the five planets known to the Greeks, Mercury, Venus, Mars, Jupiter and Saturn, was debated for decades because no planetary gearing survives. The inscriptions read in 2016 helped resolve that question, as explained below.

Dating is less precise. Estimates for when the mechanism was made range from about 205 BCE to about 87 BCE, and some researchers have proposed specific starting dates for its calendar in the early 2nd century BCE. The only firm point is that it is older than the wreck.

How researchers read letters 1.2 millimetres tall

Much of the writing on the mechanism was invisible. The letters were engraved on bronze plates that corroded on the seabed, and many now lie inside fragments, covered by other layers of metal and sediment. Some characters are only about 1.2 millimetres high.

The breakthrough came from imaging. In 1971 the physicist and historian Derek de Solla Price, working with Charalambos Karakalos, made the first X-ray and gamma-ray images of the gears and published his model in 1974. In 2005 the Antikythera Mechanism Research Project, including a Cardiff University group led by astrophysicist Mike Edmunds, brought a large X-ray computed tomography scanner to Athens and combined its three-dimensional scans with high-resolution surface imaging that reveals faint marks under shifting light.

Reading the scans slice by slice, the team spent more than ten years assembling the inscriptions. By 2016 they had read around 3,400 characters, a large increase on what had been known before.

What the 2016 inscriptions revealed

The texts are not an instruction manual. As the researchers explained, they describe what a viewer sees on the dials rather than how to operate them. Even so, they changed the picture in several ways.

The planets were on display

The inscriptions name the planets and refer to their motions, confirming that the front dial once showed them. CT scans also revealed the numbers 462 and 442, which match the cycles used to model Venus and Saturn.

Eclipses came with colours

The eclipse dial’s notes appear to describe not only when an eclipse would occur but also its colour and other qualities. That surprised the team, because it hints at an omen-reading tradition: in the ancient world, the appearance of an eclipse could be read as a sign of things to come. Edmunds said researchers were not sure how to interpret it.

A workshop, not a lone genius

The lettering appears to have been made by more than one hand, suggesting a family workshop or business. Clues in the texts point most strongly to the island of Rhodes, a centre of Greek astronomy, though that origin is still a working hypothesis rather than a certainty.

A modern working model built to show how the gear trains could have moved the dials. Photo: Andrew Barclay/Flickr (CC BY-NC 2.0). Main image: Jaysmark/Flickr (CC BY 2.0).

A teaching device about the cosmos

For a long time the mechanism was presented as a pure science instrument. The inscriptions suggest a more mixed character. Alexander Jones, a historian of ancient science at New York University and a member of the team, argued that it was not a calculating tool for working astronomers or astrologers. Instead he called it “a philosopher’s instructional device”, something to show people how the heavens fit together and where humans stand within them.

Edmunds also stressed that the formal, careful lettering makes it unlikely the object was a mere novelty. Yet he was candid about the limits of the evidence: “We still don’t know what it was for.”

That fits what ancient writers tell us. The Roman orator Cicero described sky-modelling machines attributed to Archimedes and later to the philosopher Posidonius, who taught on Rhodes. Most scholars doubt that the Antikythera device is one of those specific machines, but the descriptions show that such objects existed, were admired, and were associated with philosophical teaching.

Myths and what the evidence supports

“It was centuries ahead of its time, so it must be mysterious or impossible.” It is extraordinary, but it grows out of real Greek mathematics and Babylonian eclipse records. Its builders used cycles that astronomers had observed and tabulated for generations. What is lost is the wider tradition of such devices, not the knowledge behind them.

“It predicted the future.” It predicted regular astronomical events, such as eclipses, because those follow repeating cycles. The colour notes show that people also linked eclipses with omens, but the gears themselves only calculate.

“We now know exactly how it looked.” Not quite. Reconstructions, including a detailed computer model published by a University College London team led by Tony Freeth in 2021, combine the surviving evidence with educated inference, especially for the missing planetary gearing on the front. A good rule when you read about the mechanism is to separate what is physically visible in the fragments from what a reconstruction proposes. New readings can sharpen the picture without settling every detail.

If you visit Athens, the fragments and their replicas are worth seeing in person. Standing in front of the corroded wheels, it is easier to appreciate both the skill of the people who made them and the patience of those who spent decades learning to read them.

Sources: Wikipedia: Antikythera mechanism; Cardiff University: Research sheds light on ancient device (2016); Archaeology Wiki: Scientists closer to identifying the mechanism’s purpose (2016); IFLScience (original report). Photos: Jaysmark/Flickr, Garrett Ziegler/Flickr, Andrew Barclay/Flickr.

Related: