Determining what a computer is seems like a fairly simple thing. A laptop: yes. A piece of chocolate cake: no. A PC: sure. Sean Connery: probably not, but it's not out of the question that he could be a robot.
Then again, comparing what we know as a computer and an analog computer is a bit different. An analog computer, according to the Wikipedia, is a form of computer that uses electronic or mechanical phenomena to model the problem being solved by using one kind of physical quantity to represent another.
And that brings us to the Antikythera mechanism, which appears to be some type of clockwork mechanism and quite possibly the first analog computer ever built. The Wikipedia article says it was probably built around 87 B.C. by the Greeks, was discovered in 1902 and is thought to be the oldest known surviving geared mechanism. What's even more amazing is the fact that it uses a differential gear, which was thought to have been invented in the 16th century.
Why is this important? Who knows, but it seems fascinating that archaeologists are still uncovering the knowledge of past societies, yet even today, we cannot be certain that Sean Connery really is not robot from some prior civilization.