In 1900, sponge divers sheltering from a storm near the tiny Greek island of Antikythera found a shipwreck on the seabed, about 45 metres down. It was full of treasure: bronze and marble statues, glassware, pottery, coins.

The following year, among the finds, someone noticed a corroded, shoebox-sized lump of bronze and wood, which had split into pieces. Inside, there were gears.

A machine that shouldn't exist

For decades, nobody knew what it was. Gears with tiny triangular teeth? From an ancient Greek shipwreck? It seemed impossible.

The British historian of science Derek de Solla Price spent years studying it, and in 1974 published Gears from the Greeks, arguing that it was an astronomical calculator. But the fragments were so corroded that much remained guesswork.

Then, in 2005, researchers brought new tools: high-resolution X-ray computed tomography and advanced surface imaging. They could suddenly see inside the fragments — gear teeth, hidden layers, and thousands of tiny inscribed letters.

What it did

Turn a hand crank on the side, and the mechanism moved dials showing:

• the position of the Sun and Moon in the zodiac
• the phase of the Moon, with a little rotating ball that was half silver, half dark
• the timing of solar and lunar eclipses, using an 18-year cycle Babylonian astronomers had discovered
• a four-year cycle of athletic games, including the Olympics

It even modelled the way the Moon speeds up and slows down in its orbit, using a clever pin-and-slot arrangement between two gears.