The Antikythera Mechanism: http://bit.ly/fm4oFK is the oldest known scientific computer, built in Greece at around 100 BCE. Lost for 2000 years, it was recovered from a shipwreck in 1901. But not until a century later was its purpose understood: an astronomical clock that determines the positions of celestial bodies with extraordinary precision. 

In 2010, we built a fully-functional replica out of Lego. 

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via engadget.com