The Antikythera mechanism is an ancient analog computer designed to predict astronomical positions and eclipses. It was recovered in 1900--01 from the Antikythera wreck, a shipwreck off the Greek island of Antikythera. The computer's construction has been attributed to the Greeks and dated to the early 1st century BC. Technological artifacts approaching its complexity and workmanship did not appear again until the 14th century, when mechanical astronomical clocks began to be built in Western Europe.

The mechanism was housed in a wooden box about 340 × 180 × 90 mm in size and comprised 30 bronze gears (although more could have been lost). The largest gear, clearly visible in fragment A, was about 140 mm in diameter and had 223 teeth. The mechanism's remains were found as 82 separate fragments of which only seven contain any gears or significant inscriptions.

Today, the fragments of the Antikythera mechanism are kept at the National Archaeological Museum of Athens.