What, will the line stretch out to th' crack of doom?
Act IV, Scene 1 · Macbeth
Context
Macbeth watches a vision of eight kings pass before him, realizing they are all descendants of Banquo, and despairs at how long Banquo's line will reign.
Analysis
The metaphor of a 'line' that 'stretches out' plays on two meanings: the royal lineage and the visual line of kings Macbeth is watching file past. The phrase 'crack of doom' (Judgment Day) suggests this line will last until the literal end of time, making Macbeth's own reign feel tiny and pointless by comparison—all his murders have only secured the throne for someone else's descendants.
Essay Tip
Use this to argue that the vision of Banquo's line is the ultimate negation of Macbeth's ambition—the imagery of infinite extension ('to th' crack of doom') shows him that he has done all this violence for nothing, because his own legacy ends with him.