When Dimitrios Kondos and his crew of sponge divers found the Antikythera shipwreck in 1900, they weren't trying to make history or upend archaeologists' understanding of high technology in the late 1st century BC. They were mostly killing time.
The crew made some dives off the Greek island of Antikythera while waiting for favorable winds to continue their journey toward North Africa. While diving, they spotted a shipwreck. A recovery mission in 1901 yielded a hefty stash of statues, sculptures, and coins, putting the site on the proverbial map. All of these things happened well before anyone realized the expedition had also returned with incontrovertible evidence of the world's first analog computer: the Antikythera Mechanism.
The Antikythera Mechanism consists of some 82 fragments today, but only roughly a third of the original device is believed to survive. Researchers have known that the device was a calendar for decades, but understanding that an object represents a calendar and understanding how exactly how it was constructed are two different things. This is especially true when said object represents a level of manufacturing sophistication that European civilizations wouldn't achieve again for another 1000 – 1400 years.
Functionally, the Antikythera Mechanism is a type of orrery, a mechanical model of the solar system that shows the procession of various planets and moons over time. The device once contained a complex system of gears that modeled both the five planets known to antiquity as well as the epicycles those planets were believed to follow. [...]
Over the last few decades, a number of projects have attempted to intuit new details about the Antikythera Mechanism and how it functioned. In 2005, researchers used X-ray computed tomography to decode new, previously invisible details about the back of the machine. Dr. Tony Freeth worked on that project nearly 20 years ago, and he led the most recent attempt to intuit exactly how the Antikythera Mechanism was originally constructed.
The scientists who have attempted this task over the decades are not without some idea of what the device looked like. We know the dimensions of the box in which the mechanism was originally kept, which usefully constrains its size and physical dimensions. There are fragments of an "instruction manual" on the front and back inside covers of the box. As Freeth et al write, however:
Our challenge was to create a new model to match all the surviving evidence. Features on the Main Drive Wheel indicate that it calculated planetary motions with a complex epicyclic system (gears mounted on other gears), but its design remained a mystery. The tomography revealed a wealth of unexpected clues in the inscriptions, describing an ancient Greek Cosmos9 at the front, but attempts to solve the gearing system failed to match all the data. The evidence defines a framework for an epicyclic system at the front, but the spaces available for the gears are extremely limited. There were also unexplained components in Fragment D, revealed by the X-ray CT, and technical difficulties calculating the phases of the Moon. Then came the discovery in the tomography of surprisingly complex periods for the planets Venus and Saturn, making the task very much harder.
If the model Freeth et al have advanced is accurate, it means scientists throughout the 20th and 21st century have finally teased apart the specific functions the Antikythera Mechanism provided. In doing so, they've given us a more accurate idea of what knowledge traditions it drew on. One of the coolest facts about the Antikythera Mechanism is that the gearing that tracked the progression of the Moon properly modeled the fact that it travels at different speeds at different points in its orbit. The ancient Greeks didn't understand complex orbital dynamics, but they found a way to accurately model behavior they couldn't (correctly) explain.
Having an accurate model of both what the Antikythera Mechanism did and how it did it is a scientific breakthrough—so long as the new model stands up to long-term scrutiny.
Tony Freeth, David Higgon, Aris Dacanalis,et al. A Model of the Cosmos in the ancient Greek Antikythera Mechanism [open]. Sci Rep 11, 5821 (2021). DOI: 10.1038/s41598-021-84310-w