The Antikythera Mechanism
In 1901, Greek sponge divers working a Roman-era shipwreck off the small island of Antikythera, between Crete and the Greek mainland, brought up a lump of corroded bronze. Inside it were gears. Nothing else with comparable gearwork survives from the ancient world, and for decades the object was the poster child for anyone arguing that the ancients had help.
Modern scanning has turned it into something better: a fully documented Greek machine. In 2005 the Antikythera Mechanism Research Project imaged all 82 known fragments with X-ray computed tomography. The 30 surviving bronze gears drove dials that tracked the sun and moon, predicted eclipses through the 223-month Saros cycle, followed a 19-year lunar calendar, and even tracked the four-year cycle of athletic festivals such as the Olympic Games. A pin-and-slot device mimicked the moon's speeding up and slowing down. In 2021 a University College London team published a reconstruction of its lost planetary display.
The machine speaks for itself, literally: its dials and covers carry Greek inscriptions, and its month names come from a Greek regional calendar. Scholars date its making to the second or early first century BC, and the ship probably sank not long after 70 BC. The real lesson is not that someone else built it. It is that Hellenistic astronomers and craftsmen were far more sophisticated than the surviving texts let on.
Verdict: SolvedReal and astonishing, but its Greek inscriptions, Greek calendar and Greek astronomy show exactly who built it; nothing about it is impossible for its time.