(also dark ages) the period of European history from the fall of the Roman Empire in the West (ad 476) to about 1000, typically perceived as a time devoid of culture or, learning, or civilized attitudes

Her intellect reached forward into the twentieth century; her social prejudices and family affections reached back into the dark ages — George Bernard Shaw

(also dark ages) any period or existence seen as similarly primitive or deprived

For in those dark ages, even all-perfect America read rubbish — Louisa M Alcott