A 2,100-year-old "computer" found in a Roman shipwreck may have acted as a calendar for the Olympic Games, scientists report in Nature journal.
The Antikythera Mechanism has puzzled experts since its discovery by Greek sponge divers in 1901.
Researchers have long suspected the ancient clockwork device was used to display astronomical cycles.
A team has now found that one of the dials records the dates of the ancient Olympiad.
This could have been to provide a benchmark for the passage of time.
The device is made up of bronze gearwheels and dials, and scientists know of nothing like it until at least 1,000 years later.