Greek sponge divers exploring a shipwreck off the island of Antikythera recovered a corroded bronze mechanism in 1901 that archaeologists initially catalogued without recognizing its significance. Decades of study revealed it to be an extraordinarily sophisticated geared device, likely built around 100 BC, capable of predicting eclipses and tracking planetary positions, a level of engineering unmatched for over a millennium afterward.
The wreck itself had been found the previous year by sponge divers working the waters near the tiny island of Antikythera between Crete and the Greek mainland. Archaeologists and the Greek navy mounted a salvage operation, and among statues and amphorae, workers hauled up an unremarkable-looking lump of corroded bronze that sat in storage for years before anyone grasped what it was.
It took X-ray imaging and gear-tooth counting, much of it done by physicist Derek de Solla Price in the 1970s and later by international research teams using advanced CT scanning in the 2000s, to reveal the object's true nature: over 30 interlocking bronze gears forming a hand-cranked mechanical model of the cosmos, tracking the sun, moon, five known planets, and even predicting lunar and solar eclipses using cycles borrowed from Babylonian astronomy.
Nothing of comparable complexity appears again in the historical record until medieval European astronomical clocks over a thousand years later. The device has forced historians to radically revise assumptions about the technological sophistication of Hellenistic Greece, and researchers still debate details of its function and original appearance today.