An uncertain term used by Treebeard, apparently referring to the time that Middle-earth was under the dominion of Morgoth. It was in the Great Darkness before the Sun and Moon that Melkor bred the Orcs and the Trolls, so that these creatures feared sunlight and shunned it. The Darkness described by Treebeard was not dispelled by the coming of the Sun: Morgoth held his fortress of Angband for centuries afterwards, and even after he was overthrown, the Darkness lingered (even at the time of the War of the Ring, remnants of the Great Darkness could still be found in the deep valleys of Fangorn Forest, and elsewhere).