The Antikythera mechanism: an ancient Greek calculator

Antikythera is a small, rocky island between Kythera and Crete. In 1900 sponge divers from the island of Symi found an ancient ναυάγιον, a shipwreck, on the sea bed near its coast. In 1900 and 1901 the Greek Archaeological Service and the Greek navy brought up its cargo. It was the beginning of underwater archaeology in Greece.

The ship was a large cargo ship. It sank sometime between about 75 and 50 BC, probably on its way to Italy. It carried bronze and marble statues, such as the famous bronze “Youth of Antikythera”, as well as glass, jewellery, beds and amphorae.

Among these treasures were a few shapeless lumps of corroded bronze and wood. At first nobody paid much attention to them. Then, from 1902, researchers at the National Archaeological Museum in Athens, such as the archaeologist Valerios Stais, noticed something strange: small wheels with teeth, like the inside of a clock. This was the Antikythera mechanism. A second phase of diving, in 1976, was helped by the ship Calypso of the French explorer Jacques-Yves Cousteau, and research at the wreck still goes on today.

The mechanism was a wooden box with bronze plates on the front and back. Inside, many bronze gears, toothed τροχοί (wheels), turned one another. When the user turned the mechanism by hand, pointers moved on the dials.

Today it is broken into 82 fragments, and only about a third of it survives, including 30 gears. Scientists have used X-ray scans to look inside. They think that it showed:

• on the front, the positions of the Sun, the σελήνη (Moon) and the five πλανῆται (planets) that people knew in antiquity, around a circle of the zodiac;
• on the back, an ἡμερολόγιον (calendar) dial based on a 19-year cycle of the Moon and the Sun;
• a dial for the ἔκλειψις (eclipse), based on a cycle of 223 lunar months, which warned when eclipses of the Sun and Moon could happen;
• a small dial with the four-year cycle of the great games, with the names ΟΛΥΜΠΙΑ, ΠΥΘΙΑ, ΙΣΘΜΙΑ and ΝΕΜΕΑ.

The plates were covered with thousands of tiny Greek letters. Part of this text was a kind of user manual, which explained what the display showed.

In 1959 the historian of science Derek de Solla Price wrote an article called “An Ancient Greek Computer”, and newspapers still call the mechanism “the world’s first computer”. This needs care. It was not a computer like a laptop: it had no electricity, no memory and no program that could be changed.

Scientists describe it more exactly as an analogue astronomical calculator, an ὄργανον (instrument) of gears. Each answer was built into the number of teeth on its wheels. For example, if one wheel turns once while another turns many times, the two can copy the different speeds of the Sun and the Moon across the sky. By turning it, the user could move forward or back to any date and read where the Sun, the Moon and the planets should be.

It was still an astonishing μηχανή (machine). It is the oldest known device that turned scientific theories about the sky into moving gears. But not everything in modern models is certain. The front, with the planets, is badly damaged, and reconstructions such as the one published by a team at University College London in 2021 fill the gaps with careful but debated proposals. Some researchers have even asked whether all the fragments come from one single device.

Nobody knows who built the mechanism, and its date is debated. The National Archaeological Museum dates it, with its inscriptions, to about 150–100 BC, from the shape of the letters. A study of the eclipse dial in 2014 argued that its cycle starts in 205 BC; the authors stressed that the device itself could have been made later.

Two places are often linked with its science. The Roman writer Cicero tells of a sphere made by Archimedes of Syracuse that showed the Sun, the Moon and the planets, so some scholars think of a workshop that continued his tradition. The museum also points to the island of Rhodes, where the philosopher Posidonius taught. The games dial gives clues too: next to the four great games it names the Naa of Dodona and probably the Halieia, games of the Sun held on Rhodes. These are reasonable theories, not proofs.

Today the fragments are kept in the National Archaeological Museum in Athens, next to the statues from the same wreck. They are too fragile to travel, so new research is done with scans and with working models made of bronze, wood or computer graphics.