It’s a faux pas in some intellectual circles — mostly conservative ones — to say that there was a Dark Ages in European history.
But the mainstream view has been that the Middle Ages were a dark period in Western history. What were the “Middle Ages” in the middle of? Between the Greco-Roman era and the Renaissance. Roughly a millennium. The evaluative claim is that the glories of Greece and Rome and the achievements of the Renaissance and early Modernity were outstanding. By contrast, the Middle Ages look dimmer or actually dark.