A lump of bronze from the sea
In 1900, sponge divers sheltering from a storm found an ancient shipwreck near the small Greek island of Antikythera, between the Peloponnese and Crete. Recovery work in 1900 and 1901 brought up marble and bronze statues, pottery, glass and other cargo. Among the finds was a corroded lump of bronze, which later broke into several pieces, and it was set aside until it was noticed that it contained gear wheels.
The ship is generally dated to the first century BCE, and the device it carried is thought to be somewhat older. The date in the title, 100 BCE, is a convenient round figure, but estimates for the construction of the mechanism span roughly the second and early first centuries BCE, and scholars still debate the exact time.
What it is
Today the main surviving fragments are in the National Archaeological Museum in Athens. There are about 80 pieces in all, from a device that was once perhaps the size of a shoebox, housed in a wooden case. Within it were many bronze gears, with the surviving fragments including around thirty gear wheels, all with hand-cut triangular teeth. There were also dials and inscriptions in Greek.
It was operated, so far as researchers can tell, by turning a hand crank or knob, which drove a train of gears and moved pointers across scales. It is therefore a calculating or modeling device, in the same broad family as later mechanical calculators and clockwork, but there is no evidence of a link to medieval clocks.
How it was studied
The early work was done by examining the fragments by eye. Later studies used imaging that could see inside the corroded masses.
- The historian Derek de Solla Price studied the device from the 1950s, used X-ray photography in the early 1970s, and published an influential description of its likely gearing.
- In the early 2000s, an international team that came to be called the Antikythera Mechanism Research Project used high-resolution X-ray computed tomography and surface imaging. This revealed many previously unreadable inscriptions and gear details, and the results were published from 2006 onward.
- Further work has continued since, including new modeling by research groups in Britain and elsewhere.
The advances came from technology as much as from reading ancient sources: without modern imaging, most of the internal structure would remain hidden.
What it appears to have done
Based on the gears and inscriptions, researchers have reached broad agreement about several functions.
- A calendar. The front dial showed the position of the Sun in the zodiac and a calendar scale. A moving pointer indicated the date.
- The Moon. The device tracked the Moon’s position and phase. The Moon’s speed varies across the sky, and the mechanism seems to include a pair of gears with an offset pin and slot that reproduce this uneven motion, which is a sophisticated feature.
- Cycles. The back of the device carried spiral dials. One is linked to the 19-year Metonic cycle, after which lunar phases fall on the same calendar dates, and the 235 lunar months it contains. Another is linked to the Saros cycle of 223 lunar months, used for predicting when eclipses might occur.
- Games. A smaller dial is associated with the cycle of Panhellenic athletic festivals, including the Olympic games, a detail reported in 2008.
Statements that it “predicted” eclipses should be read carefully. The Saros dial appears to have flagged time periods in which an eclipse was possible, and the inscriptions seem to give extra information about them, but it was not a precise forecasting device.
What is still uncertain
Many questions are open.
- Planets. Inscriptions mention planets, and some researchers think the front of the mechanism showed them. A proposal published in 2021 by a team based at University College London described a possible arrangement of gears for the planets, based on the surviving evidence and a fresh reading of the inscriptions. It is a plausible reconstruction, not a settled fact, because much of the relevant part is missing.
- Who built it. The maker is unknown. Names such as Archimedes and Hipparchus have been mentioned, but there is no firm evidence. Some historians point to a possible link with the astronomical traditions of Rhodes, though that remains a hypothesis.
- Where it was going. The ship’s route and the destination of its cargo are uncertain, and so is who owned the device.
- How common such instruments were. It is the only artifact of its kind to survive, but ancient writers such as Cicero mention devices that modeled the motions of the heavens, suggesting there were others.
Why it matters
The mechanism shows that Greek-speaking craftsmen of the Hellenistic period could design and build complex systems of gears, and that they combined astronomical knowledge, possibly from Babylonian records, with fine metalworking. After it, no comparable geared device is known for well over a thousand years, until the astronomical clocks of medieval Europe, although the surviving record is too incomplete to say there were none.
Research continues, and the picture may well change as more is learned. The device is a reminder of how much ancient technology has been lost and how little of it is preserved.