The first mechanical computer was designed but never built.
Why it is true
In the 1800s, Charles Babbage designed the 'Analytical Engine'. It was too complex for the technology of his time, but his notes contained all the elements of a modern computer.
Source: Technology History
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.