"Now of old the name of that forest was Greenwood the Great, and its wide halls and aisles were the haunt of many beasts and of birds of bright song; and there was the realm of King Thranduil under the oak and the beech. But after many years, when well nigh a third of that age of the world had passed, a darkness crept slowly through the wood from the southward, and fear walked there in shadowy glades; fell beasts came hunting, and cruel and evil creatures laid there their snares.

Then the name of the forest was changed and Mirkwood it was called, for the nightshade lay deep there, and few dared to pass through, save only in the north where Thranduil’s people still held the evil at bay.”—The Silmarillion, Of the Rings of Power and the Third Age