The central theme of Julius Caesar is tyrannicide: the play asks whether it is legitimate to kill a man to prevent an evil that has not yet happened, and shows what the murder provokes. Around it turn power, loyalty and betrayal, honor, fate, and the power of words.
The question is born with Brutus. In Act II, scene 1, he admits that he has no personal grievance against Caesar and kills him for what he could become once crowned. In the play, however, Caesar never becomes king: the crown he refuses at the Lupercal is recounted by Casca, who thinks he wanted it but admits he did not pay attention.
What follows occupies the rest of the play. Over Caesar's body, Antony prophesies civil fury in Italy and, in the Forum, turns the people against the conspirators with words. In Act IV, he, Octavius, and Lepidus mark who must die, and Brutus and Cassius are defeated at Philippi, while the play closes with Octavius's order.
Other threads run alongside. Brutus replies that "not that I loved Caesar less, but that I loved Rome even more," and it is Antony, the enemy, who calls him the noblest of the Romans. Cassius says that the fault is not in the stars but in ourselves, and at Philippi he comes to give partial credit to omens. And the poet Cinna is attacked by the mob only for bearing the same name as a conspirator.