One of the earliest known analog computers is the Antikythera mechanism, an ancient device found submerged off the coast of Greece. Experts date the device somewhere between 2104 and 2222 years old, depending on who you ask.
The mechanism was composed of a complicated series of interlocking brass gears, connected to seven needles, each corresponding to one of the seven astral bodies known to the ancient Greeks: the sun, the moon, and the five inner planets. The device had additional readouts for two calendar systems. With no technology more complex than connected pieces of metal, the device was able to pinpoint the locations of all seven bodies in their orbits, and to track the phases of the moon.
The remains of the Antikythera mechanism are scattered and broken, but modern astronomers and archeologists have proposed several arrangements for the mechanism’s gearing. The latest reconstruction was built in 2012, but new proposals for the mechanism’s true gearing will probably continue to emerge for many years to come.