In 'Romeo and Juliet', Romeo flees to Mantua after killing Tybalt. The city becomes his place of exile after Prince Escalus bans him from Verona.
Romeo kills Tybalt in Act 3, Scene 1, soon after Tybalt fatally wounds Mercutio. Romeo initially refuses to fight Tybalt because the secret marriage has made Tybalt his relative, but Mercutio's death changes his attitude. Romeo pursues Tybalt and kills him, triggering the Prince's sentence.
Friar Laurence arranges for Romeo to spend the night with Juliet before escaping to Mantua. The plan depends on Romeo eventually learning that Juliet's apparent death is part of a sleeping-potion scheme. However, the message never reaches him. Romeo instead hears from Balthasar that Juliet is dead and travels back to Verona, leading to the tragedy in the Capulet tomb.
Mantua is therefore more than a destination: it represents Romeo's separation from Juliet and the dangerous communication failure that drives the final act.