The "Dark Ages" is term that the Rationalists of the "Enlightenment" period made up to describe the Middle Ages, or Medieval period (sometimes called "The Age of Faith")-- an Age that included such luminaries as Marco Polo, Geoffrey Chaucer, Francis Bacon, Thomas Aquinas, Dante, Boccacio, and others. The Rationalists made up this term to arrogantly differentiate themselves from those that came before them, just as the "Enlightenment" is actually a name they gave to their own time.
It is similar to how some modern atheists refer to themselves as "brights" to imply that if you are not an atheist, you are stupid.