The Antikythera mechanism is an ancient, intricate machine found in a shipwreck near Greece that dates back to about 100 BC. The Antikythera mechanism contains gears and structures that were not found in devices again for 1000 years, and only then when the Muslims and Chinese were busy inventing, while the Europeans were killing each other.
Popular belief was that it was made by the Greeks due to its instructions all being in Greek, but serious research published in serious places suggested the design came from Sicily.
The mechanism was supposedly used to figure out astronomical positions. The problem with that is that at the time this thing was made, no one had yet discovered laws of gravity or how heavenly bodies moved.