AI Finally Rebuilt the Antikythera Computer’s Missing Half—What It Calculates Will Shock Historians

🌌 The Clockwork of the Cosmos: The Antikythera Revelation

The sea is a keeper of secrets, a vast, indifferent archive where the most profound achievements of lost civilizations can rest, undisturbed and unknown, for millennia. On the floor of the Aegean, where the wreck of an ancient Roman freighter lay scattered, one such secret waited: an artifact of staggering complexity, a clockwork cosmos that defied every expectation historians held for the limits of ancient technology. This was the Antikythera Mechanism, an analog computer designed to predict astronomical events, a device so far ahead of its time that its equal would not be seen again for nearly 2,000 years.

🌊 A Discovery of Bronze and Dread

The spring of 1900 on the Aegean Sea was not dedicated to archaeological quests but to commerce. A crew of sponge divers from the island of Symi, led by Captain Demetrios Condos, found themselves anchored off the small, rocky island of Antikythera. Forced to wait out a patch of bad weather, they decided to dive.

It was Elias Stadiatus, descending to a depth of roughly 150 feet in the heavy, pressurized suit of the era, who first encountered the lost world. What greeted him was a vision of terror: twisted shapes and forms tangled together in the gloomy seabed. Convinced he had stumbled onto a mass grave, his blood ran cold, and he yanked his signal line, shooting to the surface in a panic. But the “bodies” were not corpses; they were statues, colossal bronze and marble figures frozen mid-fall in the wreck of a massive ancient ship.

Condos followed, and when he surfaced with a piece of undeniable proof—a bronze arm, green with centuries of corrosion—the world of archaeology changed forever. This was the start of the first organized underwater excavation in Greek history. Over the next year, the Greek Navy and divers worked tirelessly, recovering an astonishing cargo: marble masterpieces, fine glassware, coins, and countless broken artifacts.

In 1901, the crates of treasure were unpacked in the National Archaeological Museum in Athens. Among the astonishing riches lay a small, unassuming lump of badly corroded bronze and rotted wood. It was dismissed as mere debris, an unimpressive chunk of junk that sat ignored for months. Then, on May 17, 1902, museum scholar Valerios Stais spotted something extraordinary peeking through the mineralized crust: a bronze gear with teeth. This discovery was the moment the door opened to the greatest puzzle in archaeology: the Antikythera Mechanism.

Dating back to several decades before the ship’s sinking in the first century BC, the mechanism was a machine more than 2,000 years old. What survived were 82 fragments, a mere third of the original. Yet, these fragments preserved over 30 interlocking bronze gears, each tooth meticulously cut by hand. These fragments, housed in the Athens Museum, became the hard boundary of all future study: what was physically there, in bronze, teeth, and faint inscriptions, must be the starting point for imagining what was lost.

🔎 Speaking Through Silence: X-rays and AI

For decades, the mechanism was a tantalizing ruin, the rear gears whispering of astronomical cycles, but the front remaining a blank canvas. The fragments were simply too corroded to be properly understood. The real leap forward came in 2005. A joint British and Greek team brought cutting-edge imaging technology to the museum.

One device, a 12-ton computed tomography (CT) scanner nicknamed the “Bladerunner,” blasted high-energy X-rays through the fragile bronze from every angle. This allowed cross-sections to be stacked into a highly detailed three-dimensional view of the gears hidden deep within the lumps of corrosion. Simultaneously, a reflectance imaging system virtually relit the surface, pulling out faint scratches and engraved text invisible to the naked eye.

Over two weeks, this meticulous work revealed not just the internal complexity of the gears, but also thousands of text characters on the plates. For the first time in millennia, the machine spoke through its own inscriptions, revealing the technical manual and astronomical data that guided its function.

The process of decryption was slow and painstaking. Even the advanced 2005 scans had glitches, leaving blurred sections where clarity was most needed. In 2018, a University College London (UCL) team returned to the raw data, using reprocessing techniques to correct distortions and fill missing scan slices. This refinement brought new letters into focus, proving that a single Greek character could change the entire interpretation of a cycle or flip the meaning of an astronomical prediction.

Most recently, Artificial Intelligence models, such as DeepMind’s Ithaca, have been deployed to help restore broken Greek inscriptions. While not perfect alone, the AI’s predictions, when combined with human expertise, raised accuracy from 25% to over 70%, narrowing the guesswork and tightening the design requirements for the missing parts. The goal was to reach the integer ratios—the exact planetary relationships—carved into the surviving cover plates, requirements that dictated the mathematics of the missing front half.

📆 The Inscribed Back: Predicting Eclipses

The back of the mechanism survived best and offered a clear view of its core functions. It was, primarily, a sophisticated calendar and eclipse predictor.

Metonic Cycle: The upper dial was a spiral winding five times around, marking 235 lunar months. This 19-year cycle was essential for keeping the Greek lunisolar calendars aligned with the seasons.

Saros Cycle: The lower half featured a 223-lunar-month spiral, the famed Saros cycle used for predicting eclipses. Nested within this was a smaller dial tracking the Exeligmos, a 54-year cycle that corrected the awkward 8-hour remainder in the Saros period, ensuring eclipse timing stayed precise.

Cultural Markings: Another small dial marked the four-year intervals for the Great Panhellenic Games. Furthermore, the inscribed month names on the Metonic dial did not match the Athenian calendar but belonged to the Corinthian family, suggesting the device’s origin lay in Western Greece, possibly the Apirate calendar. This was the maker’s subtle civic signature.

Zooming closer to the Saros spiral, the practical nature of the device became clear. Each cell that might contain an eclipse carried a small glyph. A letter signaled whether it was Lunar ($\Sigma$ for Selinē, the moon) or Solar ($\mathrm{H}$ for Helios, the sun), followed by a time stamp and warnings—such as “of the day” or “of the night”—to indicate whether the eclipse would be visible from Greece. Index letters beneath the glyphs pointed to explanatory texts detailing the shadow’s direction, the magnitude of the eclipse, and even expected color cues. This was a user manual inscribed in bronze, a device that allowed a user to turn a crank, flag an eclipse, and read off its type, timing, and full description.

⚙️ Rebuilding the Lost Front: Engineering the Impossible

The front of the mechanism was the grand, missing challenge—the half that displayed the motions of the classical planets: Mercury, Venus, Mars, Jupiter, and Saturn. The cover plates survived, inscribed with lists of the exact synodic cycles and revolutions that the internal gear trains had to reproduce. This was not a request; it was a non-negotiable engineering requirement.

The first person to prove this was more than a theoretical exercise was Michael T. Wright in the early 2000s. Wright, a curator at the Science Museum in London, handbuilt working models using techniques known to the ancient Greeks, such as epicyclic gearing (small gears orbiting larger ones) to capture the planets’ non-uniform motion, and the pin-and-slot device to smoothly accelerate and decelerate the follower gear. He demonstrated that the front could physically carry the required planetary motions using the ancient toolkit.

The decisive breakthrough came in 2021 when the UCL team unveiled their complete architectural model of the front side. Their design adhered to three strict constraints simultaneously:

Mathematical: Reproduce the exact period relations from the inscriptions.

Spatial: Fit inside the physical clearances of the surviving bronze frame.

Mechanical: Allow all shafts and tubes to pass through the middle without colliding.

A Masterpiece of Miniaturization

The UCL model placed a small dome for Earth at the center, surrounded by concentric rings for the moving celestial bodies. This design was elegant, reducing parallax (the difficulty of reading multiple, overlapping pointers) and matching what the surviving text described as a cosmos arranged “in rings.”

A core innovation was the Central Coaxial Output (CCO)—a bundle of thin, nested tubes at the center that allowed multiple planetary displays to share the same hub. Another brilliant move was the relocation of initial drive gears for the Sun and outer planets (Mars, Jupiter, Saturn) to the front of the main circular plate. This eliminated the need for awkward, bulky brackets, opening up space and giving each planetary train a clean, direct path. The whole system was a masterpiece of watchmaker-level packing.

For instance, the surviving large fragment preserves a main drive wheel with sets of pillars, forming a sandwich structure. The UCL design meticulously packed nine closely stacked layers of gearing—including the lunar node mechanism and the base of the inner planet trains—into a space of just 0.59 inches.

The model was anchored by the subtle clues of the fragments. A mysterious hole in a block on Spoke D was solved: it was a bracket used to route a mean sun feed across the central gears to the lunar phase device, providing the necessary input without duplication. Similarly, Fragment D with its 63-tooth gear was identified as the epicyclic core of the Venus train, its riveted disc carrying the offset pin for the pin-and-slot mechanism required to model Venus’s characteristic irregular motion. In total, the 2021 reconstruction added 34 new gears to the 35 known surviving ones, for a total of 69 gears—a number tight enough to fit within the surviving physical frame.

The rebuild elevated the debate from speculation to practical engineering. Computer simulations in 2025 tested the model against real-world problems like manufacturing errors and friction, confirming the core layout but raising new questions about the Greek’s actual gear tooth shapes and precision. The mechanism was no longer a legend; it was a machine that worked, at least on paper and in simulation.

🔭 The View from Antiquity: A Living Sky

With the missing half rebuilt, historians could finally ask: What did the Greeks actually see when they looked at this machine?

The front face was a cosmic theatre, displaying nine different readouts at once: the Moon, the Lunar Nodes, Mercury, Venus, the Sun, Mars, Jupiter, Saturn, and the calendar date.

At the fixed center sat the tiny Earth dome. Around it, the six slim planetary rings were stacked, each carrying a bead representing the celestial body.

The Moon: Its pointer showed its position in the zodiac, and its phase was displayed on a marble-sized ball, half painted black and half white, which turned day by day to show every shade from new moon to full moon. The device also calculated the moon’s age (the number of days since the last new moon) by comparing the moon’s pointer to the sun’s position.

The Sun: A golden bead glided around the zodiac ring. The sun’s position instantly indicated the season, marking the solstices and equinoxes at a glance.

The Planets: Each planetary ring carried its bead, but also markers for key astronomical events: conjunctions (when a planet is near the sun), oppositions (when outer planets are opposite the sun), greatest elongations (for Mercury and Venus), and stations (when a planet seems to pause and reverse its path). When a bead hit a marker, the user knew the exact phase of the planet’s cycle.

The Dragon Hand: A special, serpent-like pointer tracked the Lunar Nodes, the two points where the moon’s orbit crosses the sun’s path. When this hand slid beneath the sun’s bead, the machine flagged that an eclipse season had arrived.

The mechanism was also an almanac. Fixed scales around the moving rings held the Parapēgma, an ancient list of seasonal sky events like the first dawn rising of a star (heliacal rising) or the last evening setting of a constellation. By checking the Sun’s position against index letters on the zodiac, the user could look up the corresponding celestial event on rectangular panels. Farmers, sailors, and travelers relied on such markers.

The Antikythera Mechanism was more than a calculating tool; it was a fully functional, highly detailed representation of the ancient Greek view of the cosmos. By reconstructing its lost half, historians and engineers did not merely fill a gap in the archaeological record; they fundamentally rewrote the history of science, proving that the ancient world possessed a mechanical genius that we are only now, two millennia later, fully grasping. It was a spectacular device, a testament to a level of mathematical and mechanical sophistication that has justly earned its place as the world’s first-known analog computer.