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.
Tony Freeth, a member of the Antikythera Mechanism Research Project, said he was "astonished" at the discovery.
"The Olympiad cycle was a very simple, four-year cycle and you don't need a sophisticated instrument like this to calculate it. It took us by huge surprise when we saw this.
"But the Games were of such cultural and social importance that it's not unnatural to have it in the Mechanism."
The technique of X-ray computed tomography gave the researchers a 3D view of its 29 surviving gears. High-resolution imaging provided them with a close-up of tiny letters engraved on the surface.
The device's "subsidiary dial" was once thought to be a 76-year "callippic" calendar.
However, Mr Freeth and his colleagues have now been able to establish from its inscriptions that it displays the 4-year Olympiad cycle.
Instead of one Olympics as there is today, the ancient Olympiads, called the Panhellenic Games, comprised four games spread over four years.
The four sectors of the dial are inscribed with a year number and two Panhellenic Games: the "crown" games of Isthmia, Olympia, Nemea and Pythia; and two lesser games: Naa (held at Dodona) and a second game which has not yet been deciphered.
In addition, the team was able to identify the names of all 12 months, which belong to the Corinthian family of months.
Corinth, in central Greece, established colonies in north-western Greece, Corfu and Sicily, where Archimedes was established.
Archimedes, whose list of exploits included an explanation for the displacement of water and a screw pump that bears his name today, died there in 212 BC.
The Antikythera Mechanism was "almost certainly made many decades" after his death, according to Alexander Jones, a professor at the Institute for the Study of the Ancient World in New York, US.
If it came from Syracuse, the dial could have been made by the school of scientists and instrument-makers he inspired.
The priceless artefact was found by a sponge diver amid other treasures on a wreck near the tiny island of Antikythera between Crete and the mainland. It is on display at the National Archaeological Museum in Athens.
This connection to the Olympics is a bit of a 'stretch', although this does seem to be new (cf. the extensive report in the New Yorker from last year); it seems misleading to suggest the purpose of this was to calculate the date of a festival which would have been 'dated' itself on the basis of a solstice vel simm.. Rather, the Olympic festival (and others) would have been a benchmark to establish the accuracy of the other dates (the journalists seem to envisage everyone having one of these and cranking the gears, waking up one morning and saying 'oh, it's the Olympics today ... see you later mom') ... the Archimedes connections seems tenuous as well (I'd be more convinced of that if it were found in/near Sicily) ... the full article in Nature is definitely interesting reading ; here's what it says on the Olympiad dial:
The subsidiary dial (Fig. 3) inside the Metonic spiral was formerly believed to be a 76-year Callippic dial8 (Supplementary Box 1). We have now established from its inscriptions that it displays the 4-year Olympiad cycle—a suggestion made previously for the main upper back dial19. The four sectors are inscribed anticlockwise with each sector containing a year number and two Panhellenic Games: the 'crown' games of Isthmia, Olympia, Nemea and Pythia and two lesser games: Naa (at Dodona) and a second game not yet deciphered20, 21. As biennial games, Isthmia and Nemea occur twice. The Olympiads were a common framework for chronology, with years normally beginning in midsummer. But here the year must start between early autumn and early spring, because the Isthmian Games are in the years preceding their usual positions in the cycle (Fig. 3). Several month names favour a start following the autumnal equinox. The small (approx8°, that is, one month) offset of the dial took account of the variation in the start of the lunisolar calendar and so ensured that the next Olympiad year would never start before the current year's games were over.
The Olympiad dial must be turned from the existing gearing6 at a rate of one-quarter turn per year. Underneath the Olympiad dial are the remains of an isolated gear with 60 teeth1, 6. Engaging this with a single additional gear with 57 teeth on the shaft of the Metonic pointer provides the correct anticlockwise rotation. Sizing this gear, with tooth pitch equal to the 60-tooth gear, gives a gear radius exactly as required by the interaxial distance: strong supporting evidence both for the Olympiad dial and this mechanical arrangement. The "76 years" inscription (Fig. 1) and other factors favour a Callippic dial, as a second subsidiary, symmetrical with the Olympiad dial—though loss of evidence means confirmation is unlikely. Might a fourth subsidiary, symmetric with the Exeligmos dial (Figs 1 and 2) complete the dial system? An existing shaft here does not penetrate the back plate and does not appear to rotate at any meaningful rate. So this seems doubtful.