The climax of a work of literature is the point at which the action and/or tension of the plot reaches its peak. The exposition (introduction) and rising action lead up to the climax, which sets the stage for the falling action and resolution. The climax is the highest point of action and usually occurs about halfway through a work.
The climax of William Shakespeare's Romeo and Juliet is seen in act 3, scene 1. In this scene, a street brawl takes place and has dire consequences for Romeo and Juliet.
Mercutio and Benvolio are approached on the street by Tybalt and his friends. Romeo enters the scene, and tensions are high between the two groups. Tybalt challenges Romeo to a fight. Unbeknownst to Tybalt, Romeo is married to Juliet. Romeo now considers Tybalt family and does not want to fight him. When Romeo once again refuses to fight, Mercutio decides to fight Tybalt in his friend's place.
All of this leads up to the climax: Romeo steps between his friend and cousin-in-law, and Tybalt stabs Mercutio under Romeo's arm. Mercutio dies after cursing both the Montagues and Capulets. Enraged by the death of his closest friend, Romeo kills Tybalt. The street brawl and deaths of Mercutio and Tybalt mark the highest point of tension and action in the play.
The climax sets the stage for the falling action and resolution. Romeo is banished from Verona for killing Tybalt. His banishment sets in motion a series of events and misunderstandings that end with the titular lovers killing themselves.