Crack of Doom

The phrase at the crack of doom, meaning "at the striking of the fateful hour", appears in Macbeth by William Shakespeare and has entered common usage. On the heath the witches show Macbeth the line of kings that will issue from Banquo:

'Why do you show me this? A fourth! Start, eyes!

What, will the line stretch out to the crack of doom?

Another yet! A seventh! I'll see no more:'

In J.R.R. Tolkien's fantasy world of Middle-earth, Tolkien plays upon Shakespeare's familiar phrase, to provide the literal Cracks of Doom (or Crack of Doom), physical cracks— fissures within the great volcano Mount Doom— the very place where the Dark Lord Sauron created the One Ring. They also are the place that the One Ring must be cast into in order to be destroyed, thereby destroying Sauron.