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. Astronomers in antiquity believed that the planets moved in circular orbits, but the geocentric, perfectly spherical models of planetary motion popular at the time could not account for the retrograde planetary motion we occasionally observe from Earth (retrograde apparent motion occurs when a planet appears to move backward in the sky).
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.
According to the authors, they’ve created the first model that plausibly demonstrates all of the known functions of the Antikythera mechanism. This is the kind of claim that might seem impossible to verify given how little of the device we still possess, but the authors argue otherwise, saying: “What has struck us forcefully in making the present model is just how few these options are: the constraints created by the surviving evidence are stringent and very difficult to meet.”
What follows in the article is a dozen-plus pages laying out how Freeth and his team assembled their model for how the complete Antikythera Mechanism must have functioned. If the idea of calculating the most probable design for a complex system of gears under nigh-impossible conditions appeals to you, you will seriously dig this paper.
According to the authors, the assembled machine may have looked something like this:
Freeth and his colleagues don’t claim that they’ve reconstructed the literal, exact Antikythera Mechanism, but they believe theirs is the first reconstruction that fully describes what the machine was capable of while simultaneously offering a cohesive, practical model for how it was built.
Unknown Unknowns, Finally Known
The existence of the Antikythera Mechanism is a humbling reminder of how little history is actually preserved in the historical record. Scientists of the early 20th century were gobsmacked by the device’s existence in part because it doesn’t look like a one-off or the sole example of its type. First-generation prototypes tend to have a lot of metaphorical wires hanging out the back and feature the occasional liberal application of tape. The initially unassuming lump of rock divers fished out of the ocean was once a highly finished product.
Archaeologists believe there was more than one Antikythera Mechanism built along similar lines. The Roman statesman Cicero wrote a description of a device that may have been an orrery, claiming that Archimedes had designed two of them and that they were brought to Rome by the general Marcus Claudius Marcellus in 212 BC. While neither of these devices is thought to be the literal Antikythera Mechanism, it could be that the ancient Greeks were building similar devices 200 years before the one we were lucky to dredge out of the Mediterranean is thought to have been constructed.
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.